Actually, I have updated the doomday timeline where Mama Longneck is spared. It's even grimmer now.
Land Before Time (original) events
Scenario 1: Littlefoot does not wander off. Sharptooth goes after Cera instead of both Littlefoot and Cera. As Littlefoot does not call for his mother, as he is still asleep, Sharptooth eats Cera for a late night snack. Sharptooth continues on his reign of terror afterward, killing and eating more dinosaurs the rest of his evil life. (Note, the events after this are the same as Scenario 2.)
Scenario 2: Littlefoot and Cera are chased by Sharptooth. They are rescued by Littlefoot's mother, who is able to dodge being mortal wounded by Sharptooth. Sharptooth may or may not have been killed (if he isn't, he will kill again over and over for the rest of his life.) The Great Earthshake happens. Herds are separated. Littlefoot remains with his alive mother and never meets Cera, Ducky, Petrie, or Spike. Cera may have met the others and led them. They likely would have followed Cera to the Mountains that Burn, where Ducky, Petrie, and Spike would not have been saved by Littlefoot, who never met them, and hence perished in lava. Cera, unable to be rescued by the others, would have become a snack for Domeheads. Littlefoot is the only main character left of the five now and comes to the Great Valley with his mother. However, he is dismayed to see that, unlike what his mother thought, there seem to be few longnecks to play with and, having never met Cera, Ducky, Petrie, and Spike, may have been a believer in herd separation and hence had few friends.
Land Before Time II: Great Valley Adventure events
- As Cera, Ducky, Petrie, and Spike have died, Littlefoot wasn't awoken by them and slept through the night. Ozzy and Strut meanwhile, unbothered by the kids, most of whom have died, are able to get eggs without being hampered.
- As Littlefoot slept through the night, Chomper's egg wasn't moved. They never became friends. Chomper hatches and stays with his parents. He becomes a regular sharptooth, learning to eat the meat of other dinosaurs.
Land Before Time III: The Time of Great Giving (events)
- With all of the gang dead, except possibly Littlefoot, Hyp wans't rescued and died in the tar pit.
- Members of the Great Valley may have died without the help of Cera, Ducky, Petrie, and Spike, Hyp.
- Without Hyp, Ducky, Cera, Petrie, and Spike, Littlefoot, Nod, and Mutt may have been unable to repeal the Fast Biters and died too.
Land Before Time IV: Journey through the Mists (which may have come before Land Before Time III chronologically) events
- Littlefoot and Ali set out alone, as they actually did in the regular universe Land Before Time, and try and get the Night Flower to save Grandpa Longneck. However, without the help of the others, Ali is unable to break the rocks after the earthshake alone. Littlefoot and Archie are killed and eaten by Dil and Ichy.
- Not getting the Nightflower, Grandpa Longneck succumbs to his illness and dies.
- Ali has some explaining to do to Littlefoot's mother and Grandma Longneck of why Littlefoot will never be coming back. The two older longneck's mourn the deaths of both Littlefoot and Grandpa Longneck.
- It is possible that Grandma Longneck and Littlefoot's mother may have left the Great Valley with Ali's herd, as Grandpa Longneck and Littlefoot are dead. If they did, there will be no more longnecks left in the Great Valley.
- Ali spends the rest of her life haunted by the death of Littlefoot, likley beating herself up for agreeing to take him toward the Land of Mists. The two have no hope of falling in love now as Littlefoot is dead.
- Ali also, alternatively, could have gone through the rocks and met Dil and Ichy and died as well.
Land Before Time V: The Mysterious Island (events)
- with Littlefoot and the gang dead and without Grandpa Longneck, the herds would undoubtably have split up, many may have died of hunger and thirst, and it is unknown how many, if any, would return to the Great Valley as they wouldn't have found all of the food wihtout the children's efforts.
- Chomper continues to eat meat and continues on his path to be a regular Sharptooth
- Plated Sharptooth lives to kill for the rest of his evil life as Littlefoot & co, who are dead, never forced him to fight Chomper's parents, so he never drowned.
Land Before Time VI: Secrets of Saurus Rock events
- Events here aren't as drastic, though the Great Valley might not be that inhabited after the events of the previous movie in this altered universe. However, Topps, Grandpa Longneck, and the five main characters are dead here.
- Bad luck wouldn't have hit the Great Valley, as Saurus Rock was never broken. However, given the other events of this altered timeline, this is very small consolation indeed.
- As Grandpa Longneck is dead and Doc wold never have gone near Saurus Rock, the two sharpteeth seen in the Great Valley might still be alive.
Land Before Time VII: The Stone of Cold Fire events
- Without anyone believing that there is good in him and with no chance at redemption, Pterano would almost certainly have remained bad and, over time, become as evil as Rinkus and Sierra.
Land Before Time VIII: The Big Freeze events
- Without being able to help the children, Mr. Thicknose might not have been able to get redemption and may have fallen out of favor with the grownups and lost his teaching position.
- The Mountain Sharptooth, having never been killed by Thicknose as he'd have no reason to go into the Mysterious Beyond, would have lived and killed more dinosaurs for food.
- Tippy and his herd, having not been rescued by the others, as they are all dead, would have died of hunger in the Mysterious Beyond.
Land Before Time IX: Journey to Big Water events
- Mo, having not been helped to find his home again, may well have been killed by the Swimming Sharptooth when he got free.
Land Before Time X: Great Longneck Migration events
- Grandma Longneck goes on the journey with Littlefoot's mother. Grandpa Longneck and Littlefoot have long been dead.
- There they meet Bron, who hears the sad news that his son and father-in-law have died. Littlefoot's Mother would have lived with her husband upon finding him. Grandma Longneck, now a widow, may also have stayed with them. In this case, there would be no longnecks left in the Great Valley.
- Without Littlefoot & co being there, Shorty may not have gotten away from the orange Tyranosaurus, meaning possible death of Shorty.
- Without Littlefoot & Co, Grandpa Longneck, and possibly Shorty, alive, the fight here may have had fatalities. Possibly Littlefoot's mother and Grandma Longneck could have been among those.
- As Bron was injured from being bitten, Bron may have died in the fight as he would have had less backup.
- The male belly dragger (who may have died of hunger in the regular timeline as he got stuck), didn't get stuck here, meaning others may die at his, er, clutches, in future.
Land Before Time XI: Invasion of the Tinysauruses events
- Big Daddy and the other Tinysauruses, having never befriended Littlefoot and the others as they are all dead, will remain wary of bigger dinosaurs for the rest of their lives.
- As Topps may have died, Tria never falls in love with him.
Land Before Time XII: The Great Day of Flyers events
- The Great Day of Flyers would never have been altered by Petrie as he died years earlier.
- Tricia would have drowned
- Guido may well have fallen to his death while sleep walking/flying as the others wouldn't have been there to rescue him.
Land Before Time XIII: The Wisdom of Friends events
- It isn't known here how things may have differed, though Loofah and Doofah might have come to a bad end without the other characters being alive.
- Those sharpteeth that fell off that cliff would still be alive, meaning other dinosaurs wouldn't be in the future
TV Series events
- The TV Series would, for all intents and purposes, have been about Chomper, a leat-eater killing meat eater, and Ruby as the Gang of Five are all dead by that point.
- Had Chomper and his parents encountered Ruby and her family, Ruby and her family would have been eaten. No way Chomper and Ruby could be friends at any rate.
- As Chomper would NEVER have been let into the Great Valley, Chomper would have had to have spent the rest of their lives running around the Mysterious Beyond running from Red Claw and his Fast Biters, perhaps one day coming to a bad end at their hand.
- Skip dies in fire with nobody to rescue him.
- Belly Draggers get into Great Valley as there is no "Amazing Threehorn Girl" to stop them.
- Lydia, Milo, and Plove continue to be terrorized by the Great Hideous Beast.
- Dara dies in the sinking sand as they didn't get there in time.
- Swooper stays in the cave for the rest of his life as he never met Guido or Petrie, both of whom are dead.
- As Chomper, who kills leaf eaters still, is not welcome in the Great Valley, he was not there to save Mama Flyer, who died from suffocation in the mud. Petrie's siblings are now orphaned. As Pterano is a villain, they cannot live with him, or, if they do, are perverted to his bad ways.
- As Sauro never became the new Story Teller, the Longneck Stories may have been forgotten as Grandpa Longneck is dead and Littlefoot is no longer around to pass them on.
Post TV Series:
Assuming Chomper somehow beat or got away from Red Claw, Chomper is now a threat to the Great Valley and all leaf eaters, killing and eating them for the rest of his life.
- Assuming Ali didn't die in IV, she will marry Rhett and NOT Littlefoot. She is still haunted about the deaths of both Littlefoot and Grandpa Longneck and how she was unable to save them. (Poor, poor Ali!)
