How long does it take a decent quality speaker to "wear out"?

Have an old pair of Spectrum 208A made in Toledo,Ohio.  The firm closed in the 90s.  Recently had them re-grilled and re-foamed by a speaker guru outside St. Louis.  

Still have the same cross overs ... still surprise me!  

Until a few years ago was listening to a 40 year old pair of Vandersteens, then traded them for a 30 year old pair of Vandersteens.

No longer own them either.

Both sounded and performed as new.

Who knows when they might "wear out"?

Purchased a pair of Yamaha NS1000M speakers in 1980 and foolishly sold then 34 years latter. Still looked and played perfectly. Never had a issue with them during that time.

In 1972 when my wife and I were both in college we bought a pair of Bose 901 Series 1, the ones with the drivers having corrugated surrounds.  Now half a century later the speakers are still going strong in our son's basement party room.  The chintzy little equalizer long since bit the dirt and was replaced by an after market equalizer. 

Loudspeaker materials usually don't last forever but it's hard to wear out most speakers.