I do question Johnny's attendance record in recent seasons (at least, this season and the previous one). He's "live" on the Thursday and Friday shows (and they usually get great shots of him on the Thursday shows' intros), but he's relatively subdued during Mon-Wed shows. Furthermore, his announcing area seems to disappear on Mon-Wed shows.
That's because he really isn't present for those earlier shows. This has been mentioned over on the jeopardy subreddit. For them, Sarah from the Clue Crew will do them live and then Johnny redubs them later. So your ears (and eyes for that matter) aren't deceiving you, he really isn't at those shows. He just comes in for the final two they tape. I would almost wonder actually if the idea at least now is for Sarah maybe to assume that role after Johnny either passes or can't do it anymore, but that's only a guess obviously.
Regardless though, it's amazing to me that he has lasted as long as he has in the role. And he doesn't really even look or sound his age at all IMO. It's quite a remarkable run that will be hard to equal to say the least.
It's also as a sidenote really interesting to me, that for two different shows (one being the original Price, and the other being of course Jeopardy when it returned in 84), Johnny ended up succeeding Don Pardo in the announcing role. That's another thing I am not sure you'll ever see again, where the same person takes over the job of the same other person on more than one occasion. It seems like the odds of that occurring would be low, although I could be wrong on that.