I have played with singers, as well as guitarists, who will deviate from the expected arrangement. In the latter case, I always think of Rory Gallagher. If you watch videos of him and his band, you can see the visual (or aural) cues he gives the band. I can do 'on the fly' pretty easily but that's not the point, to me.
The bit that would have me quitting is the temper. My gig would be ruined by the expectation of trouble and I can't be dealing with that. Whether that's people complaining about his volume or any other issue that might crop up at a gig. Someone that wound up is someone I'd be avoiding. How good or great they were (as a guitarist) is irrelevant here.