It will be interesting to see a number of things following this.
1. Will they be forced to change the engine or will Microsoft provide people that can update it to actually work the way it is supposed to for Bethesda's type of games?
2. Will they change upper management to get rid of those that are negatively affecting the titles (Emil is bad for writing, Pete doesn't even like dialogue and just wants to gun shit down and would be better suited to whisper in the ears of DOOM than Fallout or Elder Scrolls and Todd is, well, Todd).
3. Some have suggested that Zenimax has been the problem. That they were the ones who dictated the direction of games and only wanted profit so milk away as much as possible. Now that Zenimax is out of the picture and Microsoft (which have been surprisingly consumer-friendly as of late) owns them, will we see a change in game design?
4. With how many studios Microsoft has now acquired will we see cross-IP usage between them?
Either way, this deal just happened and games take an asslong time to develop and Bethesda themselves are busy with three project AFAIK so sadly I doubt we'll see the impact upon Fallout any time soon and I will not get my hopes up for anything like that. It will be interesting to see if they'll remaster Fallout New Vegas though since Bethesda could never be arsed to hire anyone to do it.