I have a reasonably high number of datapoints, since I service many of our legacy products that are somewhat ancient. Typically you should expect 2A3s and 300Bs to last 5-10 years, with some slow degradation in performance as you near the end of life. For preamp and driver tubes, especially when they are old stock parts, it can be a challenge to actually wear them out.
PJ uses the first SEX 2.0 prototype amp on his TV, and he is still on the first set of tubes. I have an amp that's very similar to the SEX amp running 24/7/365 in my workshop, and it will eat through tubes about every 5 years (that's about 40,000 hours).
There are absolutely certain tube preamps that I won't name here which run their tubes well over the plate dissipation rating and sometimes also the plate voltage rating at the same time, and you can expect very short life in those products. Also big KT88/6550 amps seem to wear out the power tubes pretty quickly.
