Yes, that’s the million euro question; closed cols means either a detour or just buggering off home. Given I don’t really have any goal other than “riding lots” I will play it by ear and ride to Berlin or something if the high mountains are looking likely to be closed.
The only time I planned to go over the Galibier it was looking closed and instead of going up the Maurienne valley I went via Grenoble and over the Lauteret on the south side of the Galibier.
Not the world’s nicest road, but it gets you to the same place.
But then, to be honest, I think unless you’re really itching to chalk up a few selfies against >2000m signposts there’s arguably better riding to be had away from the high cols. The Vercors has some great stuff and if you go west of the Rhône there are some stunning places to ride in the Ardèche, the Cévennes and then south or west from there. Still plenty of testing climbing if you want it, but more varied scenery and less traffic.