Thrawn, Ezra, and Peallon have a role to play(the are most likely going to fight the FO if not then i do not know what.) in the future.
I don't exactly see how Ezra and Thrawn can have a role against the First Order in any sense. You're essentially saying that after managing to survive a hyperspace jump of unknown duration to unknown location while fighting on a depressurised bridge, both of them then manage another 40 years without killing each other before returning the galaxy at large to save the day together?
Ezra, Thrawn, Peallon, and the seventh fleet are gone, but not dead
I don't think Pellaeon is gone. In what I've read of Filoni's interview comments he name-dropped Pellaeon to restore the character to canon and leave him open for other authors to pick up, which would be hard to do if he's stuck in the same place as Thrawn/Ezra!
Saying its a happliy ever after is not really fair since their are still characters that dont have "Happy Endings."
Sure, there are variable outcomes but generally it is quite happy.
- Lothal remained free from Imperial rule or retaliation and recovered.
- Hera survived the rest of the Rebellion and brought up Kanan's child.
- Zeb returned to his people and took Kallus with him, relieving Kallus' guilt about his part in the Lasat genocide.
- Ahsoka is undead (but in an unknown location for an unknown period of time).
- Ezra and Thrawn are undead (but in an unknown location for an unknown period of time).
Aside from "where the hell are people?" I think Sabine's outcome is the most unclear. First her relationship with Ezra seems more brother/sister than anything else to me, and she was actually quite accepting of his decision to finish the mission and save Lothal. More generally however we've no idea what happened with her family back on Mandalore while she stayed on Lothal keeping her promise to Ezra (or how she understood it, anyway), which seems a big omission considering how important Mandalore has been over the last few series.