I agree with the previous poster,, that is, if the catalog is gone, it has to be re-imported to get the catalog back, I recommend that it be imported into an unused media pool
If the catalog is still present IMMEDIATELY move the media to an unused media pool so it will not be over-written
Get properties for this media, and obtain any session IDs on the media
In the GUI, go to the InternalDatabase context, expand sessions, and find the session ID(s) you noted in the previous step. Right-click on the session ID, pick Change Data Protection, and set it to Permanent
Right-click on the session again, pick Change Catalog protection, and set it to Same as Data Protection