Universe A still used-to-exist , it just doesn't-exist-in-the-future. Universe B did NOT used-to-exist, and it will continue to not-exist-in-the-future unless you chose it.

In other words, both universes don't-exist-in-the-future if you don't chose them.

I suppose I'm lost on why one would consider "Universe A ceases to exist going forward" with "Universe A is destroyed". It feels like a really weird variant of the sunk cost fallacy, since Universe B failing to exist going forward isn't a big deal.

I can see arguments about time travel being complex, it's hard to predict the results, etc., but all else being equal it seems baffling to insist on A over B just because A happened to exist in the past.