How long do high quality speakers "last"


I am the original owner of a pair of ProAc Response 2 speakers. They are almost 7 years old, but have never been driven excessively hard. How long (i.e. useful lifespan in years) can I expect these speakers to "last" (i.e. no significant sonic degradation) if I care for them carefully? When they do start to degrade, what mechanical failures and sonic degradations can I expect to occur? Thanks in advance!!!
mshan
Wondering if the OP will see this and chime in on the condition of his Response 2's now that they are roughly 22 years old.  
I have a pair of Kef C55 that were purchase about 1990 that still sound fantastic. They have taken quite a beating, too.
I expect my Silverline Preludes to really last as they have magnesium/aluminum drivers and rubber surrounds. The crossover caps may die before the drivers, but I’ll likely get bored and replace the speakers with something else due to boredom or curiosity well before any of that. Note that I use my trusty old Boston Acoustics A60IIs in my TV system and have replaced the woofers once (foam degradation). years ago…they still kick a--, so to speak (from 1988 or something?). I assume the ferrofluid will dry up eventually in the tweeters but so far they work fine.
The question responders should ask of the OP is, physically or technologically.

Larry

An important issue for me,as I'm retired and can't really afford to replace myDaedalus Audio DA-RMAs, which I love. I am reassured by remembering my first ever speakers bought in 1966, second hand, were still in use by my late lamented Mother, when she passed in 2012. Now that is'nt to bad.