I recently got a 96, for free. It has 117000 miles on it. The cargo area was nearly gone, the exhaust was falling off, and the abs was wacky. cdl frozen.The emissions light was on but no cel. It ran and was driven daily by the previous owner.
I fixed the cargo area with aluminum diamond plate, pb blasted the cdl linkage to life, new brake lines, pulled the abs fuse, replaced the exhaust, new air filter, oil change. The previous owner had said he just replaced the plugs and wires. after driving it for a while it still didn't feel quite right. I decided to check the plugs,most were crappy, cly 7 was brand new. For some odd reason, i put a code reader on it, 2 cylinder misfire codes, and the general misfire code.
replaced wires and plugs, still no spark to that cylinder, replaced coil pack, yeah!, all is good.
What sort of problems will running on 7 cylinders for a crap load of time cause? The previous owner had it for about 8 months. before that it was occasionally driven by his brother but mostly sat around.

The truck runs great now. no codes. I assume if the misfires trashed something i would be still have codes? I would expect the cat on that side to be toast, and maybe the o2 too but nothing shows up. just lucky?
Going to work my way through the 60k fix-it list, and fix the cel.

 

Running one cylinder with no spark for a long period of time will just dump raw fuel down stream to the exhaust.
I wouldnt worry about it unless a problem comes up.
Good for you on bringing this near death truck back to life.

 

It may shorten the life of the cat, but if it's not showing any symptoms, i would just keep driving it. I had a cat go bad(was making a knocking sound/falling apart) and it would throw a code for it once in a while. No code-good to go