Blackhawks are known to be tough, and rightfully so. It is a well-deserved reputation.
That being said - they CAN in fact be worn out. I bought a used New Model (DOM is 1974) from my LGS, and it was not particularly accurate and would misfire occasionally. Sent it off to Ruger and they replaced a number of small parts, springs and plungers. Also re-timed it and even threw in a new set of wood grips.
Works great now (thanks Ruger!).
I was told beforehand that the gun had been used in CAS, so I have no quarrel with my LGS. I gave it back to them for inspection when I first noticed the misfires, and they basically handed it back and said "it's probably fine". That legendary Blackhawk toughness is deeply ingrained - as you can see from this very thread. But the point is that if you shoot the living snot out of it you may have issues and no, it won't take 2 or 3 lifetimes.
I would guess that my particular specimen had at least 10,000 rounds down the tube when I got it, and probably closer to 20,000. But there is no way for me to know.