I was in his shoes.
Customers do occasionally forget to send lenses back on time. We have procedures in place to deal with that.
I'm not sure what the record for a late return is, but a couple of years ago one of our customers was "sectioned" (i.e. involuntarily committed to a secure psychiatric hospital) whilst he had one of our lenses. Of course we didn't know about this at the time. The lens sat there in his house for several weeks and we were unable to communicate with him. Eventually he was allowed home for a few hours at a time in the company of a carer, and one of the carers packaged up the lens and sent it back to us. We waived the £800+ late fee.
Sooner or later it's a statistical certainty that one of our customers will die whilst hiring one of our lenses. It hasn't happened yet - the closest call we've had (that I'm aware of) was when a customer was airlifted out of Silverstone with appendicitis. But if and when it does happen, I'm sure it will be an administrative nightmare.