I have had this happen. Passenger side bolts holding the mount to the block sheared off. the engine rolled to the passenger side and was held up by the distributor resting on the mount. Fortunately the damage was limited to that. UNfortunately the issue was discovered the week before Christmas and no one had shop space or time to effect the repairs for me.
Soooo...The Friday night before Christmas about 3 years ago I stayed late after work and working only with some hand tools, a right angle drill, some stubby drill bits that I still had to cut down more, no engine hoist, and an air compressor that kept tripping the breaker I pulled an all-nighter and drilled out 3 bolt shafts that I could not see and replaced the 3 bolts. And it only took me 14-1/2 hours.
The issue: I could not raise or lower the engine enough to get clear access to the last bolt. The frame rail was in the way. Hence the use of a right angle drill and stubby bits that had to be cut down further. In retrospect, I cannot remember whether I unbolted the driver's side mount or not. either way, it took me something on the order of 5 hours to get at and drill out/easy out the first bolt. And for the record, easyouts, contrary to the name, are NOT that easy to get broken bolts out with under ideal conditions and damn near impossible under adverse conditions.
Upon inspection it appeared that 2 of the bolts had sheared off previously and I had been running on the remaining bolt for some time. until i hit a big pothole.
The ONLY thing that was positive about the whole ordeal was the fact that the broken bolts were Grade 5 and not Grade 8 otherwise it might have taken me the entire weekend.
So, in a nutshell, if you even THINK you need to ugrade to the BrownDog mounts (or similar), Do it.
Or, at least check out your stock ones and/or remove them one by one and install new bolts with washers per Jon's write-up.
IIRC this was prevalent from 91 to 96 when the first version of the HO came out.