Check if the organizers have a backup plan for cancellations. I once saw a local band fill in and they blew everyone away. The real test of a festival is how it deals with problems.
That shift to a bar acoustic set sounds kinda perfect tbh. Reminds me of a story I read about a DIY fest in Austin where the main generator blew. They rigged up a sound system from car batteries and a boombox for the last few bands. Goes right with what @iristaylor said about the real test being how they handle the mess. Those scramble moments usually make a better story than the plan.