Been there, done that. Singer and guitarist bitch slapping each other because their egos have collided (meanwhile bass player and drummer head to the bar for a swift pint).
Played a gig recently where the guitarist had amp problems and ended up playing through my Fender Rumble 100 which I happened to have in the car. It was an emergency solution which actually sounded really good.
The irony of it is that thousands of people who've paid through the nose for tickets will doubtless spend the whole gig filming it on their phones so that they can watch it on Youtube later. Mugs.