The "get one before he retires" line has been going around for years. But I doubt that means substantially identical knives won't be available - the "lone master" image that many vendors cultivate notwithstanding, I would guess someone (an apprentice, Watanabe, other?) will pick up the hammer when he puts it down in one form or another... if that hasn't happened in all but name already.
(Disclaimer: 100% uninformed speculation, just thinking of Anryu -> Ikeda and Shiraki -> Nakagawa etc. If actually knowledge people say I'm full of it disregard.)