"Now - if the guy who said he wanted you is no longer involved, opened his mouth when he shouldn;t have or is otherwise ignoring you - will have to speak up. They think you'll be on their doorstep, expecting to perform. They'l put up or shut up."

If "the guy" is no longer involved, he's unlikely to speak up. He's somewhere else. And what makes you so certain the rest of them will put up or shut up? My suspicion is that they'll just let buddy show up, then look surprised, then tell him if wants to hang around till midnight, when all the booked acts are finished, he can play for the stragglers while the volunteers pack up the sound equipment and slam the tables and chairs around. If there's some left over food, he might even get a free sandwich.