A "journalling" file system keeps a record of filesystem transactions and a marker so it knows which ones aren't reflected in the meta information. A forced umount - say by a power failure - thus doesn't require a lengthy file system check. Instead, it finds the marker I mentioned in the journal and "replays" the journal entries. This brings the meta-data and thus the filesystem back up to date with a coherent structure.

You want an undelete. Good luck.

Wade.