Actually, the Constitution says whatever Justice Kennedy (as the “swing” justice) decides it says, since his vote generally carries the day - Kennedy is America’s omnipotent king. But you’re right about the peril remaining with the aging constitutionalists. I guess the doctrine of “stare decisis” is only applicable when a leftist decision is the one being referred to.
Generally, but not always. Roberts was the swing vote on Obamacare.
As for "stare decisis," in 1986 the Supreme Court found that sodomy is not to be a Constitutional right. By 2003, the composition of the Court had changed and suddenly sodomy was discovered to be a Constitutional right all along.
Look at every 5/4 decision that has gone the right way in the past decade. Every single one of those decisions will be reversed if Kennedy, Scalia or Thomas is replaced with a liberal.