How long do high quality speakers "last"

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.

Recently I saw a pair of Duntech Sovereign 2001's with all of the bass drivers worn due to age. The cone surrounds crumbled into dust in my hands! Now whether this was caused by sheer age, or due to excessive sun exposure I don't know...but the result is the same. Someone can probably replace the drivers...but it is going to be a project.

44 year old pair of EPI 70’s still running strong; all original including the surrounds. Pretty sure the Pioneer receiver they run on is just as old and with original lamps and no LED crap lights either... still original caps too. Original owner. My teenage son now has this in his room.