The only idea I even have for such a campaign is one where all the BBGs are dopplegangers of the party and the players are trying to defeat me, playing as their dopplegangers.
I would only be able to do what the players themselves can do. So it becomes a test of who understands the build better. The player or the DM.
The reason for your character to stay doesnt have to be something they agree with. It can be someone elseโs reason.
And โthe quest to fuck off and do something elseโ can be fun too. You seem to be working with a very authoritarian concept of game. Those can work sometimes, but are very limiting.
less friction
Not always desirable.
Our group has done this. Shot our paladin at a dragon to try to wrestle the wretched wyrm to the ground.
The wrestling part was not very effective, but we did manage to fell the beast, so we had that going for us.