Easy fix, at most 5min of work depending which method you want to use to fix it.
Method 1: Run an "oversized" 6-48 tap from the inside out. These are specialty gunsmith taps and screws made to cut a little oversized for repairing damaged 6-48 threads, so you do not need to enlarge the screw hole of your scope mount.
Method 2: Recut all four screw holes on the receiver to #8-40, making the mounting significantly stronger and keeping all the screw sizes identical and standard. Note these would need the scope base to either be modified or one made to use #8 screws.
Method 3: Countersink the top to remove the damaged threads, and use a longer (1/2" long) #6-48 screw and cut it to fit the full hole depth. Most screws provided with bases are too short anyways and usually only engage 1/3 of the threads on the thick Mossberg receivers, so this will also make a stronger mounting.
Personally I'd charge $10 for fixes 1 and 3, and $20 for 2 because of the extra screws.