Sony already has to deal with the very real prospect of not having Alex much longer (in the grand scheme of things-the show has been on 35+ years; I'm not talking "tomorrow" here). While Pat and Vanna are no spring chickens, they are under contract, and while contracts have ways of being dealt with, don't expect both shows to be upended simultaneously.
There is zero chance Jeopardy gets cancelled now. None. Whether Alex is able to return and tape new shows whenever the time comes remains to be seen. And taking his words at face value, he's not looking for an Oprah-esque farewell tour of a season. But one way or another, they're going to continue on with a new host and see how that goes. There is way, way too much money at stake to do otherwise.
Pat and Vanna may not re-up (their choice or not, who knows) for another hitch after the current deal expires, but with all other factors in mind, there's only a slightly more than zero chance of them not returning for anything other than health reasons.