amplifier longevity

Ideally in theory…
But I have had both varieties fail on me.

carver crimson 350 monos.

amazing longevity and reliability!

Bryson has issues, not often!

odyssey audio has been reliable.

McIntosh is reliable !

Not counting my first tube amp, a VTL.....I have had excellent reliability with tube gear.  My current amps are 8 years old , look and work perfect still

Assuming high quality like those 2 makers, no difference would be my answer.

Good Tube stuff is designed to handle heat, so there isn’t a lifespan issue that I have experienced. My quality SS equipment has been very reliable, it can get hot also.

My reliability issues have been with the weakest link, usually a moving part, look for them: a speaker terminal or push button breaks, a jack panel loosens, ground connection screw strips, loosens some how.

When I buy cameras, it’s also the weakest link. I try to anticipate, avoid problems, a cheap plastic battery door, waiting for me to break it. If I buy cheap stuff, or good stuff with cheap parts, I treat it’s cheap moving parts more carefully,

If one had ceramic tube sockets, the other plastic tube sockets, that's a clue.

And, modern equipment, too much complexity, too much software, i.e. for some reasons, an HDMI jack stops working, a ...

In my experiences over the decades, I have had some of both, SS and tube equipment fail. Most have been reliable. I had an instance or two of bad design that eventually led to failure, and bad parts or assembly. 
Some manufacturers are known for reliability and great sound. I won’t buy from a certain manufacturer that has good sound,  but has proven unreliable and problematic.. 

Tube amps can be very reliable as much of the hardworking parts are the tubes themselves. SS has come a long way and I don’t have to have tubes anymore ..