There are far too many variable involved that there is no meaningful answer to how long to expect speakers to last. I've heard drivers that are really old that have held up well, even without a re-coning. That is particularly the case with woofers with the pleated fabric or paper surrounds. It is far more common to see crumbling on soft rubber surrounds. Many modern speakers with such surrounds go bad in 10-15 years, while I've hear old pleated paper drivers that are 70 or more years in age.
The midrange in my system (compression driver feeding a horn) is at least 80 years old and it works fine.