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41st lv DM
Which is rolling back his past character arcs. And, hey, he's a prince: they seldom get to be who they are expected to be.
The catch is, that doesn't work for the MCU. Because then you have to wonder why Thor doesn't come back and help. Because he's a rogue warrior out there trying to right wrongs.
So why isn't he helping when the inevitable Avengers 5 happens?
Even moderately intelligent people will realize that, as Capt. Marvel pointed out on screen, it's a big universe out there.
So storywise why doesn't Thor appear? Because he's busy doing something far far away. And that might be a story we'll all get to watch later.

Instead, he needs to have his "end" in Guardians of the Galaxy Volume 3. Which feels weird, as that should be about the Guardians and wrapping up their story.
Wrong on both counts. Neither needs a "end".
What's needed is A) coherent storytelling, B) Leaving the door open for more stories involving these characters.
So Thor flying off with the Guardians here as End Game wraps? That's a great place to leave Thor. If it works out & they come up next story involving Thor & Hemsworth signs on? Great! If not? Then Thor flew off with the Guardians, parted ways with them at some point off screen, & is just off having adventures we just don't get to see. But he could return.
Likewise with the Guardians. They don't need an "end". Just a good adventure. Nor does Thor have to be with them just because we last saw him standing in their ships cockpit.
And if any of the actors don't return after G3? Then those characters are just off screen doing their own thing.