Episode? Don't you mean movie? It was in the Land Before Time VII: The Stone of Cold Fire.
The sharptooth were mainly the cause of it, but a lot of the plant-eaters panicked and perhaps fell to their deaths. It does show a parasaurlophus fall to its death.
As for if they all died, that's hard to say. The movie doesn't really show us if they did, though not a lot of them did survive, because things looked pretty hopeless for them, hence Pterano fleeing. It was said that the herd never saw any of those that followed Pterano again, but why would they? If they survived, they were a pretty fertile place, I doubt they would want to leave, no matter what kind of experience they had there.
They could have listened to him because they thought that the other's way of making decisions as a group was a bad system. The grown-ups have been shown to be somewhat slow acting (hence why Littlefoot and the gang usually have to go off and fix things themselves.) perhaps that was a factor. Or maybe it was similar to the reason that Ducky, Petrie, and Spike followed Cera, rather then Littlefoot. Perhaps Pterano's route was easier. Any number of these could have been a factor in their decision to follow Pterano.