We're heading to New Vegas in Season 2, and this is the only character I really would like to see resurface, mostly because Yes Man saved me from never finishing New Vegas. I was starting to get bored with the plot and Yes Man brought me back in.
Dave Foley killed as it Yes Man, and I would love to see him back in the role. I was a big fan of Foley from Kids in the Hall/News Radio days, and I was overjoyed when I ran into Yes Man and recognized his voice. Dave Foley has exactly the kind of absurd cheery demeanor a character like Yes Man needs.
Further, I'm going to assume the Courier/Yes Man taking over the Strip ending of New Vegas probably isn't canon, it means there's ample opportunity potentially for Yes Man to continue being the best Yes Man that he is.
Hell, I'd love to see any of the Kids in the Hall in Season 2, honestly. Kevin McDonald keeps looking weirder every fucking year, he would fit in with wastelanders. Hell, the new Kids in the Hall season was an Amazon Prime show, and both Kevin and Dave went full frontal nudity with their weird old bodies. They're the right kind of fit for the wasteland.
I would also think Foley's "Doomsday DJ" sketch is a great example of why they need him in Season 2 of Fallout.
The NCR was not just Shady Sands. It was all of California up into Oregon and into Nevada. Literally everywhere the show goes shouldn't be post apocalyptic thanks to the NCR's GECK
The show literally does not comment on whether or not the NCR still exists elsewhere. Arguably, like in real life, it's a war of attrition, where differing sides gain and lose ground in different areas at different times.
Ukraine has won and lost lots of battles, and they have won and lost ground. Just because it doesn't comment on the NCR doesn't mean that the NCR is gone, it could easily be that we're seeing one small slice of the NCR in a place where it is losing ground.
Further, this timeline is post-New Vegas, and there's a good chance that the canon ending was Mr. House succeeding in deploying his Securitron army. We don't know of other aftermath, whether he used that to destroy local NCR forces, and so on. The aftermath of a war between NCR and the Securitrons would certainly leave a "post-apocalyptic" wake of destruction.
Finally, none of that even touches on whether or not it was potentially Cesar's legion or some other currently unnamed faction who slowly broke down the NCR organization over time.
There could be plenty of valid reasons why things are so fucked in the West, and they don't all involve completely retconning everything.
Its not House since New Vegas is a wasteland.
New Vegas is a tourist-based economy. If the NCR pulled out for any reason then it'd get pretty wasteland-ey pretty quick.
Also if House is alive in Season 2 then the only possible canon ending is The House Always Wins, since every other ending explicitly leads to his death.