iOS deletes an app’s files with the app. For a vault with no account, that is the vault.
What survives
An encrypted backup in your own iCloud, if backup was on, plus your recovery phrase. Reinstall, restore, type the phrase, and the files are back. Purchases survive too: Lifetime and subscriptions restore from your Apple ID.
What does not
Anything only on the phone. If backup was off, or paused because iCloud was full, the files that never uploaded are gone with the app.
Check two things first
Open Backup: it should say On with a recent time, and Test restore should pass with your phrase. Then you can delete with a clear head. Or export everything to the Files app first; export is free.
“Offload App” is different
iOS’s Offload keeps the app’s documents and data and removes only the app. A vault survives an offload. It does not survive a delete.