All Tremoverbs (and 2-channel Dual Recs, and MkIVs etc) *potentially* have LDR issues, because they use so many of them. That isn't to say all the amps will develop them though. Mesa had a bad batch of LDRs late on in the Tremoverb production run, so I would say you're more likely to have problems with one of these, but my '94 has had four fail so far as well. (Out of 25.)
You can either have them replaced as and when necessary or do the lot in one go. It isn't a big job to replace just one, probably about fifteen minutes' worth of work (including opening up the amp and reassembly) once you've identified which it is - which you can do logically from the schematic, if you note which functions aren't working. Replacing all 25 would be more like a couple of hours, I would think.
The good news is that even a bad LDR failure that cuts off one of the channels will still leave the amp functioning at a gig, albeit only on one channel... so you can get by with a pedal on the functioning channel if you can re-dial it to something that works. The only LDRs that could stop both channels working are in the FX loop circuit, so you could always bypass that if you had to.
Overall I wouldn't worry *too* much about it - it's certainly a known issue, but no worse than many of the other reliability problems on many other amps, and not as common as tube failure either.
