If you back up the Repository and Data files, you can restore your databases completely. I don't know a way to backup a single cube but I have used the following to backup databases and I was able to recover them completely.
The Repository backup is easy if you have it migrated to SQL server, if not just backup the access file in BIN directory under Analysis Services. Also backup the Data directory.
Whenever you copy these files back to their right places and restart the Analysis Services, you'll have restored the status to the time you took the backup.
Shab