For Fallout 3 you do not need to run GFWL. GFWL just needs to be installed. As long as you can get and install the last version of GFWL I doubt Bethesda will make a patch for it.
As for Achievement I doubt they will add any since Bethesda are not working on those games anymore but are working on a new project.
Well for one thing, Oblivion doesn't use GFWL at all, nor does it have any sort of achievements. And frankly, I fail to see the point in achievements at all. They're a pointless addition to the game IMO. It certainly wouldn't be worth Bethesda's while to spend the time creating them for such an old game. People aren't going lay down more cash for the game simply because they existed. Most of the former players have already moved on to other games. As Erzherzoghans points out, GFWL does not need to be accessed, it only needs to be installed. And as long as Microsoft still makes the base client available on their web site, which they do, then there really isn't any need for Bethesda to take any action at this time.