How long do high quality speakers "last"

One nice thing about my ZU's is that you can purchase upgraded drivers. I purchased my Omen Defs in 2012 (update B) and they have the updated tweeter. Since, ZU has released upgraded larger drivers as well. Outside a light dusting every now and then, the drivers look and feel as good as new with no deterioration (at least from what I see or hear).

mshan, it is extraordinarily variable. Foam surrounds are always a bad sign and these hardly ever make it past 25 years. Voice coils can burn out or unravel and the driver starts making strange noises. On the other hand I have two pairs of Mirage speakers in my workshop in the worse of conditions. They are 30 years old and sound fine although they don't look so hot. A good ESL like a Sound Labs speaker will last indefinitely.  

My Thiel CS2's are 32 years old and still mint. They may outlast me.

I bought a pair of Series 1 Bose 901s (closed box, rubber surrounds) I bought in 1972.  My son still has them.  They look and play fine in his basement party room.