Heat, depending on design and how and where is used, can defiantly pose a longevity problem.
Early model Krell KSA and KST power amps notoriously failed do to cap failure from heat. Design modifications using better caps and more attention to heat dispersion solved the problem. I know of the problem with the Krells because I had them and went through the headache and expense of getting problem solved.
Not to pick on Krell, per say, as am sure that other early hi-biasing class A/AB amp manufactures had heat issues to work out as well......Jim