Here is some speculation on my part:
Littlefoot: Become the leader of the dinosaurs in the valley, marry Ali, have children, and pass his wisdom on...
Cera: Eventually find a male Triceratops who can "tame" her, although even after she becomes nicer and has children, she still has some of her old "flare."
Ducky: She will become a great mother.
Spike: He will have to learn how to talk.
Petrie: He will become a secondary leader in the valley, and be Littlefoot's "eyes and ears"; in a sense, he will be the leader Pterano wanted to be, and will be respected among the pterosaurs.
Ruby: She will eventually come to live in peace in the valley with her family.
Chomper: He will have no choice but to leave the valley, but will show up on the borders to meet with old friends occasionally.
Tops: He will be known as "Old man threehorn", and will still be himself... but will be reminded not to get too worked up about every little thing by Tria.
Tria: She will still be Tops' wife and may very well have more children with him. Still the same as before in most ways.
Tricia: She will likely grow up to be like her mother.
Littlefoot's grandparents: Still alive, but barely.
Mr Thicknose: Dead.
Bron: Still the leader of his herd, visits occasionally.
Ali: Left her herd to live in the great valley with Littlefoot, has children with him, is greatly respected as the wife of the leader.
Pterano: Returns to the valley after his banishment time is up, is initially distrusted by all, redeems himself by saving Tricia, which gives him the respect of Tops, Cera and Tria.
Ducky's mother: Still alive, has children and grandchildren...
Petrie's mother: Proud of her son, and has her other children as adults by now as well.
Some future possible scenes:
- Pterano's return to the valley.
- Littlefoot's handling of his first crisis.
- Ali (now an adult) and Tria relaxing in the mud pools, talking about how Littlefoot is the new leader and how Tops has stepped down.
- Petrie rising to a position of respect among the flyers, showing him leading them in a formation.