I`ve done em when they`ve died and the daughter or son have kept me on till the house sells.
ive had a few like that, also got a few at the moment that are in hospital,their sons or daughters phoned and asked me to continue, they send a cheque every 2 cleans or so .
also where the custy has passed away, and i've been asked to clean until house is sold , you then know when the house is sold and new people are moving in,
you can then usually get the buisiness, esp. if you ask who ever pays, to mention you are the regular window cleaner and will be calling to see if they wish to continue
daz