I've seen a few people in this sort of predicament. I would have a chat with your venue - they may be more lenient as it's clear why you picked that day in the first place, and it's not your fault that the bank holiday was removed.
Other than that, have a chat with your friends and family - they have plenty of notice if they wanted to book the day off - 3 day week for the win! Failing that, I have that day off already, I'll come to your wedding and party!
Sorry I can't be more help, it really sucks that people like yourself have been left in this position. Just chat to your venue before you panic. Good luck x