Life span of speakers

Several hundred years...
If the surrounds of the drivers can be replaced at suitable intervals.
And any capcitors in the crossovers can also be replaced.

Since speakers $$$ such as you speak of had not been made more than forty years ago.. Look at plenty of 1940's and 1950's 1960's speakers still going strong.

I second Elizabeth's comments but would add that environment makes a significant factor. If stored and used in stable interior climate conditions the life can be well over fifty years.

Speaking from experience, my 33 year old Yamaha NS1000M speakers still look and sound excellent to me.

Usually speakers in the $5000 range last about 4 to 7 years. Speakers in the $12 range last closer to 10 years..

What about electrostats?

They don't last nearly as long.