It all depends on how prejudiced against the other dinosaur races she was. Judging by how fast the herds on the other side of the divide teamed up, you could assume that she could have adapted as fast. After all, it's unlikely that she would have left Cera or any other hatchlings behind to perish.
But let's muse. If she had survived sharptooth's attack (or even returned during the scene with Littlefoot's shadow, the following would have happened.
*Cera probably would still have fallen down the crevasse, unless she decided that an adult was the best person to follow.
*Ducky might have been rescued (since Littlefoot reached the pond she was hiding at after resuming his search), but unless they stopped to eat from the same tree, Petrie might not have been rescued.
*Cera, if she fell down the crevasse, would have alerted them to Sharptooth. Whether or not they took the warning seriously here could have changed things. It is unlikely that Cera would have performed her retelling of the story to Littlefoot's mother, so unless their route went past his egg, Spike might not have been rescued.
*The Longneck herd that devoured the oasis might have met up with them, and teamed up.
*If they had camped at the oasis, Littlefoot's mother might have had to duel Sharptooth again, as she would not have been able to make it through the mountain gap the others escaped through. If she survived this, she could still follow them (Sharptooth managed to, after all).
*If Littlefoot's mother had made it so far, chances are they would have taken a different route into the mountains, meaning the fight with Cera and subsequent journey through the mountains that burn wouldn't have happened.
*Unless they confronted him at the lake, Sharptooth would have followed them into the Great Valley, where chaos would have temporarily broken out.
If the GOF survived the exodus, then the rest of the films would probably have continued as normal, except he might not be as willing to go off on an adventure, as he wouldn't have discovered the ability to survive on his own. Littlefoot's mother would have adapted to co-existing with the other herds after reuniting with Grandma and Grandpa Longneck. However, if some of the GOF were not found...
*Chomper would probably have never met the GOF. (2)
*The Great Valley might have been destroyed by the water shortage. (3)
*Grandpa Longneck would most likely have perished from his sickness, and possibly Littlefoot too, unless Ali managed to rally a rescue, and they continued from there. (4)
*Unless they met Elsie by luck, the GOF might have remained trapped on the Mysterious Island (Chomper might not have even been there). (5)
*If Grandpa Longneck perished in 4, the entirety of 6 would not have occured, save from a visit from Doc.
*If either Ducky or Petrie did not survive, then 7 would have ended with Pterano, Rinkus and Sierra perishing at the volcano, or at least with out Pterano redeeming himself.
*If Spike or Ducky hadn't survived, 8 would not have happened. In fact, if Ducky hadn't survived, Spike wouldn't be living with her family.
*9 and 10 would have largely been the same, except in 10, Littlefoot's herd might have gone with Bron at the end.
*11 probably would have happened the same.
*If Petrie didn't survive, then the Day Of The Fliers wouldn't have been as important to the GOF. Guido would still have met them, but he probably would have disappeared in the night.
*Littlefoot's actions at the start of 13 might have been different. Ultimately, it would all depend on whether his mother would catch him leaving the valley or not. The Yellowbellies would probably still have survived on their own, but their journey would have been interesting, to say the least.
Well, a lot of that's depressing. And it makes me sort of think that could be explored in an "It's A Wonderful Life" or "Back To The Future" style fic.