How long should high quality speakers last?

Forever.because they cut my grants from the gov.all of the above is great advice.there are companies that replace the ferrofluid.i have reconed many speakers and using the shims to center the cone is very important keeping the voice coil aligned. Caps do age out but can be tested bulging and leakage is not good.coils hardly ever wear outresearch and do it yourself.enjoy the music and the journey.

Dunno my Tannoy D700 perform perfectly fine since 1998

I've had my PSB Image 2B speakers for over 20 years and they still sound great.

I've had my Definitive Technology BP 30's since 2001 and they were built in 1999 and still sound as they did then that I can remember.

I have Kef 107.2 That I bought in 1990.

i had them totally rebuilt 2015 sound as good as they did new.

Refurb took almost a year.