Hi,
if it's done on the same cell server, you will not get prompted for the key, as the key is managed by DP. If you are not able try the restore from a different cell server, you would need to backup the keystore (export the keys), delete the keys, try the restore - which will fail, as no key is present). In this case you will not be prompted for a key, this happens during EADR or when importiung the media in a different cell only.
Do not forget to import the key again. All is done with omnikeytool.
However, I seriously advice to not do that with your productive cell server - for security reasons use a test server. I'm not responsible for any damage this will cause.
Best regards
Daniel