Speakers don't last as 'forever' as electronics, but, in my experience, damn near. My Vandersteens are 20 years old and going strong. I once had some advents that I sent the woofers to Florida for reconing. Far as I know the EX is still using them.
Speaker Lifespan
Barring a blown driver, tweeter, etc. How long before sound starts to obviously degrade? I have Mirage Bi Polars that are 12 years old. Not looking forward to replacing them.