nice news, I hope everything keeps going well for the couple
personally I don't think ZUN's to-be wife will interfere directly with the series' universe, though I can imagine that, with the coming of a family, the games (and musics and written works) will take longer (unless he gets enough people to help him in production and he finds himself time). It's even possible that he somehow decides that making games/music/writings isn't as much fun anymore, or he doesn't have as much time as he would like to and find himself unable to do (in his words, previously) games that he'd like to enjoy.
This said, I personally think that the man deserves his happiness, and I'm thankful for the stuff he's made so far, which gave the fanbase something (especially diverse and likable) to be creative with. I didn't mention, too, but there's also a more 'neutral' outcome, or even something better than initially expected, production-wise. There should be no reason for us to worry about, since there's not something that's under our control (partially or completely). Once again, I'm just playing with the possibilities
(especially one where ZUN's children do what Tolkien's couldn't do well, afaik: to take the reins of the IP and continue his legacy. Or... ZUN stops making Touhou works and agrees to concede the IP or rights of use to Cave, due to not being able to attend to doujin conventions anymore. Or even gives them some help and participation.)
Lastly, I'm curious if we'll ever see his future wife make games as well, and if she does, what kind of games would they be like.