Trumpite replacement candidates have been losing close congressional seats to Democratic challengers so this may open up some pathways to retaking a majority.

Exactly. The ones that are closer to being moderate (there are currently no moderate Republicans in the house) are leaving. They're less crazy in general, so not only are there fewer Republicans to push back against the MAGA crowd, it leaves spots open to be filled by even crazier Republicans.

Yeah, I feel like the sinking ship is a "sane Republican party". We're just going to see more Boebert's, MTG's, and Jim Jordan's in Congress now, which will lead to even more dysfunction and gridlock.

The fact that there's even a debate to be had about whether it's a victory just shows how fucked up our system of government is—in this case, our electoral processes. Government policies in a democracy should be highly predictable based on what's popular with the voting-age public, but instead, the policy effects of something as minor as some people retiring are so unpredictable we may as well be trying to read the future in chicken entrails.

Both can be true at the same time. The system itself is broken, and the fact that it allows fascists to gain so much traction is a symptom of that brokenness.

why put themselves at risk confronting the problems in the party, when they can just leave, with their money and influence, and let the crazies run the nuthouse

Yeah, but they'll be safe, because they were a Republican once, right? Right‽

More importantly, flee rather than fight the crazy

There really aren't any moderates.