Everyone commits money by a deadline. Enough people: it's GO. Not enough: everyone gets their money back, guaranteed by Solana. No organizer can run off with it, no refund forms.
Pay the ticket, or lock a small deposit, into a vault owned by the event. Not by the organizer. Backers can chip in money without taking a seat.
Headcount (and budget) reached by the deadline? It's on. The organizer gets paid; at the door, attendees scan the door screen and their deposit comes back.
Missed it? Everyone refunds themselves on-chain. Backers can pay for the pizza, but they can't fake the headcount.