Good question!
Other than the driver surrounds crumbling, I have never had a speaker “Wear out” I have upgraded crossovers because it was an upgrade, not because of any other reasons.
How long does it take a decent quality speaker to "wear out"?
After all, they do have moving parts and capacitors. . . .
(I suppose that "decent quality" s a relative term. FTR, I am running a pair of the older B&W 805s, and for all I know, they may not actually meet the criteria of "decent quality.")