If the drive units have non foam surrounds, twenty years plus. Beyond that, some crossover components might need refurbishment. That's assuming the speakers are driven within normal parameters - not used as PA for parties. That's for moving coil speakers.
How long should high quality speakers last?
My Zu Omen Def MKii (rev B) are going on 13-14 years old. The speakers sound wonderful. I have no intention of parting with them. The speakers came with the latest ZU tweeter design. How long should I expect the speakers to last without any issues? I do not abuse the speakers and run them with my Luxman 595ase amp.