I like to think Marvel is smart enough to realize that it’d be in poor taste to kill off T’Challa less than a few months after his actor in a separate universe died. Plus he still technically has a book (and likely relaunch) so I don’t think he’ll die anytime soon. Plus, Namor is a mutant, if he dies this arc it’ll be easier for Hickman to resurrect him and integrate Atlantis into what he’s doing with the X-Men.
I wouldn’t say Aaron’s reignited the rivalry between them. Their conflict this run has been surprisingly impersonal. Namor’s petty so obviously he made I think a reference or two to the Wakandan destruction of Atlantis but other than that T’Challa’s looked at him as just another threat in a wider network of villains the Avengers gotta deal with. But I agree it wouldn’t surprise me if they end up going head to head. T’Challa’s been used prominently this last arc and it’d make sense considering the role of the Phoenix in their recent histories.