In my entire lifetime (45 years), I've known of only two sizes of cylindrical cells ever to go off the market.
Those are the E cell (from "701" 3V cycle lamps) and the BF (927 or No.8) cell from handheld bedside torches.
Every other size of cell is still in production.
Even B cells are still made, if you are happy to crack open 4.5V cycle lamps!
None of these cells EVER enjoyed the popularity, widespread use or market pentration of the CR123A, so the latter should be around for many years to come.
But - even if they do, it would present an excuse for buying new flashlights, wouldn't it?