A more appropriate reply to your query might be to look to your BEX setup and consider what happens when BEX target media failes. If you have a standalone tape drive and it fails, no backup. If you have a cascaded drive pool with multiple tape drives, expect BEX to failover to the next drive simply because it is available. (assuming scratch tape loaded, on-line, etc.)
If you haved backed data up to your NAS, the BEX save sets should be visable there. If you have those save sets on tape they could be restored to your NAS (post repair and assumming connectivity, etc.).
If BEX could not select the new copy of the save set using its old catalogs, you would need to catalog each restored save set on NAS.
I'm not sure how BEX would react to (and how you would reliably select) the catalogs to delete. I've recently discovered that BEX 10.0 will allow identical media labels in a media set (I'm sure the internal labels are different). It's hard to quickly determine which tape is which from the catalog.
Pick a save set on NAS. Delete it. Restore it from tape and see what happens. Shouldn't bee too hard to test without waiting for your NAS to ralph a hairball.