With the renewed interest from the show, it would make sense for Microsoft to get someone else working on a Fallout game since Bethesda isn’t going to do it any time soon. However, I would think that Obsidian would be the more natural choice. I would guess that MS would prefer to utilize one of the studios they own rather than license it out, but I could be wrong about that.

And even if they did license out development on a Fallout game, I would assume that they would be in a hurry to get something out there, which would make Larian far less appealing to them. I agree that they would probably make an amazing Fallout game, but another studio would probably make a decent enough game that costs less to develop and pays off sooner.