Pterano and Petrie's relationship is my favorite thing about the seventh film. We rarely see the main characters interacting with members outside their immediate family (parents, siblings, etc) so I think it was a refreshing change to make Pterano to be Petrie's uncle instead of a father.
I see Pterano as a grey-area character - he's too good to be bad, and too bad to be good - and he has redeeming qualities, but at least in the film they are overlooked by his greed for power. I don't think it was a wise move for the adults of the Great Valley to banish Pterano away. If he stayed there, they could've monitored his behavior better, intervene if something shady was going on, and most importantly, I think it would've been good for him to stay in contact with his known family instead of spending time with sleazebags like Rinkus and Sierra. Momma Flyer would definitely keep him in line, and Petrie obviously has a positive influence on Pterano. I sincerely think that he could've started to straighten his behavior if not for himself, at least for Petrie.
On the other hand, being punished and spending time alone gives Pterano time to gather his thoughts and reflect upon his actions. Then he can make the decision if he wants to change his behavior, strive for better and return to his family, or if he prefers his life in the Great Beyond as it is. Judging by his character, I see both as feasible choices for him, but personally I prefer him returning back and rekindle his familial relationship with Petrie and the rest of the family.
Petrie has grown and matured when Pterano comes back, and I don't think he idolizes his uncle as much as he used to. Of course he's happy that Pterano is back and is probably the only one in the Valley to be excited about it, but Petrie doesn't put him on a pedestal anymore. It's easy for me to imagine that Pterano has calmed down and doesn't have plots and plans to cause mischief in the Great Valley. Maybe he's old and tired and just wants to find a place that feels like home. And I think Petrie could be a key factor in Pterano redeeming himself and others finding him a threat no more. Or, if not completely redeemed (I don't expect anyone to forgive him for the sh*tty things he has done), at least accepted by the community.
Pterano is a father figure to Petrie. Petrie looks to him to know what to become when he grows up, which complicates things because Pterano is cult leader, who led many astray.
I think calling Pterano a cult leader is a strong but false claim. He became a leader of a small group of seven dinosaurs who agreed with him. He really thought he had the answers and that the path they took was correct, and he led his group to a sharptooth ambush by accident. It wasn't his goal to put his herd in harms way and Pterano is shown to feel remorse and survivors guilt for that incident. There were no religious connotations in the flashbacks or anything reminiscent of cult behavior - no mind-altering practices to suppress doubt, no alienation from society, no threats of leaving the group, no abuse, no unquestioning commitment to the leader. Just because Pterano's opinions were different from the likes of Grandpa Longneck, it doesn't make him a bad person inherently. Literally the reason why the adults don't like him is that he took no responsibility for the mistake he made, for breaking up the herd and endangering those who decided to follow him.
