Well he would still own the IP if he made a new Fallout game. As per the agreement with Bethesda Herve Caen had a few years to retain the IP but he failed to make said game.I'm calling Herve Caen right now….!
Oh wait, he doesn't own the IP anymore.
Nevermind, I'll let Bethesda do it's thing.
Doesn't stop him from popping up and trying again though under a different name.