Hi OP, I'll throw you a line and say yes! yes, comeuppance does happen.
I wrote about horrible experience at work three years ago, from two evil unpleasant cows. Started the only thread I've ever created. Got 30 or so supportive comments which really helped, but I was really cut up by it, long campaign that culminated with real nastiness - as I obviously wouldn't be managed out quickly enough.
I'd worked my arse off, was good at what I did, and tolerated some real incompetence from my two managers but they were vile. I walked away.
Three years later, and a few short term contracts behind me, I have not just landed a great job, I have landed my weirdly specific dream job.
In the meantime something nasty has been uncovered at old workplace and the evil twins are in massive trouble
I have been contacted to be a witness for some crappy behaviour but I just can't be bothered, all behind me now.
OK, maybe it's not karma, but they heard of my fantastic news, how senior to them I now am (which will piss them off hugely) in the same week the shit hit the fan for them. Karma, coincidence, whatever, but delicious timing so really feels like a comeuppance.
People that crap will find their shitiness catches up with them. Its hard I know, but don't let the bastard get you down.