1st, as suggested by Mike, call the support and they’ll be able to assist you. That’s an emergency and they’re handful for such.
DDB is only used to backup.
From what I understood, you just need to restore data, not to backup.
So, of course, you’ll get tons of warning/critical errors from the Commserve/MA logs reporting a ddb or devices are down, but this should not prevent your disk library to be back online, if it had been brought up exactly as it was before the issue.
The devil lies in the details, and maybe here in your MA where you have you disklibrary, the LUN IDs could have changed, the windows disk IDs (SAN mostly equals to multipathing so after a hardware failure paths could have changed also), resulting in data inside the volume is OK, but from a topdown hardware volume point of view, the device hosting this volume(s) for Commvault is not exactly the same. Then Commvault reports that disk library as offline.
In this disk library, do you have more than 1 mount path ?
What is the status of the mount path : is it offline ? Enabled ? Compare this and details to the physical volume inside the OS.
And also make sure for this MA that all backup, pruning, data aging activities are disabled until situation is solved and you recovered your data.