I'd say 50% chance that he reappears in the new French government within a week. Timing is too good not suspect something like that.
For that, he'd just resign. This is airing the dirty laundry.
Why not hitting two birds with one stone if the opportunity's there?
The EU is a dead end for him as Von der Leyen has been reappointed so now is a good time to quit because he has another opportunity in France (my guess).