I had wondered that myself. It's one of those mysteries of television. He wad never even MENTIONED. It's like he never existed.
That happens on many shows, where the character is written-out of the series and never heard from or mentioned again.
MASH did that with some of the early "side" characters, like
on Law & Order, though there were transition episodes at the start of the next season with a successor (Ben Stone departing, Jack McCoy arriving), in some cases, two prominent characters in the early seasons suddenly disappeared:
-Asst. to the DA Paul Robinette. Suddenly, Jill Kincaid, the new DA asst., arrives with no explanation as to what happened to Paul (except for years later when he's in private practice).
-Capt. Cragen. Same as above.
And lets not forget Chuck Cunningham from Happy Days