Bruce's voice is not a problem. I mean, in 2022 he closed the set with Aces High, which is difficult for a 20 years old. All in standard tuning.
I don't think Bruce will lose more high notes at this point, but even in that case, they can still drop the tuning and he wouldn't has the smallest problem.
Nicko, on the other hand, is another matter. I'm sure he's not giving 100% every night of a tour (he said that in 1988 ) to keep the overall performance good, but he's only getting older and it's not gonna be easy. That being said, in Calgary last year Steve asked to slow down CSIT. Even after what he had Nicko is still capable of surprising.