How long do speakers last?

There are far too many variable involved that there is no meaningful answer to how long to expect speakers to last.  I've heard drivers that are really old that have held up well, even without a re-coning.  That is particularly the case with woofers with the pleated fabric or paper surrounds.  It is far more common to see crumbling on soft rubber surrounds.  Many modern speakers with such surrounds go bad in 10-15 years, while I've hear old pleated paper drivers that are 70 or more years in age. 

The midrange in my system (compression driver feeding a horn) is at least 80 years old and it works fine.

I have a pair of JSE .8 Infinite Slope speakers that I purchased in 1988 that still sound so great. I ended up giving them to my son in Philly last year when I no longer needed them in my secondary system and he loves them. They have had no reconditioning and have just been treated with some good old fashioned TLC. I heard them last month when visiting him and they still sound terrific.

@mucker , The sky is the limit with fabric just please do not do the paisley.  You will need a person competent with a sowing machine. The sock has to be made undersized so it will stretch tight putting it on. Think of putting a girdle on an elephant. 

One of the safest bets in old speakers are Magnepans. No voice coils to burn out, no surrounds to dry up and disintegrate, no fancy cabinetry to get banged up. There is really very little to damage or go wrong in a Maggie but you do have to be careful around that ribbon tweeter. 

Can you define last?   Old speakers still play and sound good, but over time the sound quality, assuming no damage, will degrade slowly.  I had a 20 year old pair of SF and they sound good, but not as good as new.  Difficult to really compare with the passage of time.  I was told the caps (or other elements) in the cross overs can go out of spec after decades and the aging rubber or what ever it is can break down a bit.