I think people got way too excited about this based on 2016. It's still somewhat less college educated and way more religious (including plenty of the college educated people) than the national average. There's also a lot of evidence Texas Hispanics are culturally assimilating toward white Evangelicals. That having been said, I don't think it will ever go back to being R+25, but there's no reason it wouldn't stay R+10ish for many years. Maybe Dems eventually win it in a 2008 scenario as a one-time thing.
What if a Conservadem wins as a Senator?
Texas doesn't really have them anymore. Cuellar is basically the last one standing and now he's under a probably career ending indictment. Texas conservadems were in terminal decline by the early 2000's and virtually wiped out in the early 2010's.
IDK maybe there's a pro-life Tejano Dem representing the RGV in the state senate who could still fill this role, but I seriously doubt it. Rural white ancestral Dem areas aren't relevant enough for a Manchin or even Fetterman type to take off.
Cuellar will be fine, honestly.
For this November probably yes but no way Cuellar survives until the 2026 Midterms and if Biden wins narrowly (I am still one of those people who thinks he will) then Cuellar is TOAST in 2026 either in a D-Primary or GE.