I saying Littlefoot,not for the reasons of the gang but for the reason he is the last of his line.
He something happens to him before he can...
you know the whole herd will die out. Which is quite tragic so not only would Littlefoot die but his whole family line. He is an only child so the only one who can carry on his family's blood.
Plus just imagine his poor Grandparents reactions to the news..naw.
But they will all be sad,
Ducky would be tragic since her first voice actor died only 10 years old and it would be like a reminder of that.