From what I remember, his mother, so far, never taught Littlefoot to distrust other species; just that they never did anything together. Also, Littlefoot's mother saved Cera's life, showing that she is willing to set aside differences to do the right thing.
I think a more likely scenario is that Littlefoot may have become less social towards other species, but may still be willing to give them a chance. I don't think he'd shy away from other species entirely.
As for Spike dying, there is really no evidence to prove Sharptooth would have been there at the time. If Littlefoot was indeed with his mother, then likely he would not have crossed the same path as he would have, which lead him and the others to meet Spike in the first place. Instead, he'd be elsewhere, thus Sharptooth, if he is still after Littlefoot, wouldn't have come across that area either. And if Littlefoot and his mother had come across Spike, chances are they would have let him travel with them. Littlefoot's mother is not cold towards other species (she saved Cera even though she didn't have to), so she probably would have let Spike travel with them just until they reach the Great Valley.
I don't really agree with Petrie not learning to fly. It is true that the battle with Sharptooth led to him flying, but, if this event had not occurred, he would have likely found another way to fly. He probably would have continued practicing to fly until he was able to do it, especially if he was determined to find his family again.
