Esker
Hero
Which in effect boils down to the same thing: play my way or go home.
I mean, said another way, it boils down to "Don't try to overturn the group's consensus about how they want to play; or find another group that shares your playstyle." Hard to argue with that, I think.
And, even if a character gets booted from a party it still a) is a character existing in the game world and b) has a player attached. So until-unless the player turns that PC over to the DM to use as an NPC that character still belongs to the player.
Narrative coherence is not of such paramount importance that a DM is obligated to spend mental effort figuring out how to work your PC's arc into the story when you as a player get asked to leave the game. Deus ex machina "they vanish in a puff of mist" is perfectly reasonable in that situation. There is, of course, nothing stopping you from taking that same character and playing them at another table (minus whatever equipment and treasure; possibly at a different level; etc).
The social contract quite rightly tells me I can't just reach across the table, haul off and punch Bob in the face. But there's absolutely nothing saying my character Eohyl can't haul off and punch Bob's character Falstaff in the face, even though Bob and I might otherwise be the best of friends.
Unless the players have agreed out of game that PCs punching each other is part of the way they want to play the game, then the default social contract for a cooperative RPG does prohibit that, yes.
Actually, yes it is; as it's the harmless shenanigans and PvP that can be (and IME are) laughed off that are what people seem to want to ban; and I'm not cool with that.
D&D is a group game. If the rest of the people at the table don't want PvP, then it's not the table for you. Nobody is saying that no group should be allowed to include PvP in their playstyle. But if the people you're playing with aren't cool with it, then yes, you're obligated to "metagame" in such a way that prevents your character from engaging in that sort of behavior. Otherwise you're being a jerk out-of-game, as much as you might want to pretend that your player hands are clean when your character's hands punch another PC or whatever.
From what you're saying, it sounds like your group is fine with it. Nobody is saying there's anything wrong with that; as long as the DM and all the players are on the same page.
But the piece about the long-term change to a well-loved character? Happens all the time as a known part of the game; the only difference here is that the source of said change might be another PC rather than something in the setting (e.g. trap) or opposition.
Again, if it's the setting or an enemy that causes something bad to happen, that's a risk that's built into the game itself. If your PC does something to another PC that causes something like that to happen, unless your group has established that as part of their social contract, then you're just being a jerk. You, as a player; not your character. And if the posts here are any indication, the large majority of groups are not okay with that crap.