How long should high quality speakers last?

I know someone with a pair of original Western Electric 753 speakers.  They are both probably from the late 1940's to early 1950's.  They sound really good.  He also has a pair of Western Electric 757 speakers from the same era that I also like very much.  

Your Omen Def’s don’t have a cross over just a cap on the tweeter. The 10” drivers are reported to be indestructible. There are two kits available from ZU if you want to upgrade them to match the Omen Def Supremes which I have. One is an upgraded tweeter with an upgraded cap for said tweeter. The other is a wide plinth that perfectly sets the air gap for the ports under the speaker and provides a more stable bass. 

I had a pair of Ohm Walsh speakers last over 30 years and was used daily. I did replace the drivers after the 30 year mark with an upgrade kit from Ohm. 
As long as it is in a normal humidity and temperature environment it will last longer than you might think.

@paradisecom I have Bozaks from 1963. Replacing the capacitors in the crossovers definitely improved the sound quality.

I just gave my brother a pair of Heresy II.   Still work and sound good.   I'm guessing they are 35-40 years old.