Just like Ramesh I have run into the situation where the Broker-pers file has gotten corrupted. The only recovery we were able to do at that point was to send the corrupted file to wM support and they sent us back the equivalent of an adl file that could be viewed in a text editor.
One BIG warning to using backups though. It is not necessary to backup the broker-pers to save design-time development work. There is no design-time development information stored in the broker-pers file. For design-time information such as event types and other configuration the broker-guar is used.
Now to the warning. If you backup a broker-pers on a nightly basis and then use it to recover after a corrupted broker-pers, then you will run the risk of redelivering any persistent events that were stored in the broker-pers file at the time of backup. You should be able to handle any such duplication of data in your process without corrupting your resources.
Worst of all, trying to recover from backed-up broker-pers file will cause you too loose any eventes that were queued at the time of corruption.
My recommendation is that you stay away from persistent storage. Use guaranteed for canonical events and volatile for everything else (within reason).