The real money with these stadia comes from selling out the VIP section. Their budget forecasts will take a hit as they're not gonna be getting high occupancy at high prices there. Plus the TV and rights money that they're missing out on, the stadium will be budgeted based on that.
Bums on seats is a small part of the income nowadays, and those bums will have cheaper tickets in the championship.
It would definitely be a terrible time for them to be relegated.