Isn't this what some refer to as burn-in? I would expect that the actual mechanical operation of headphone drivers stay well below levels at which permanent changes occur in the materials. Change, if any, would be most significant in the first moments of usage, and then converge to zero as the headphones age.
In-ear monitors typically fail from either wax buildup in the sound port (clogging filters) or from wire or soldering problems. Driver failures aren't unheard of, but my impression is that they're manufacturing defects, not age-related failure.