1. don't panic
2. take a deep breath
3. do what jommy said:
Remember to backup the (corrupted) wallet just in case.
Then place one of your backups in said directory and rename it wallet.dat
backups will take some 100 transactions before going out of sync, so you're probably good with your latest backup.
Anyway don't panic, if you have your backups, you're 99% fine.