I recently began to the process of digitizing family photos and thinking about the best way to keep them around for another fifty years and found myself playing with the idea of building this kind of infrastructure.
You're still relatively early in the game - on a decades long timeframe at least - but it's worth considering these kinds of policies. Your average customer is probably not savvy enough to have a preformed opinion, but from one technologist to another I find myself naturally pedantic over what "ample notice" might mean.
If you're lucky and successful you'll eventually have to deal with stuff like, "what if the user dies, and stops paying" - do you delete the data?, and how do you handle people associated with them looking to grab the info?
Having a next-of-kin login process or a "shutdown the webview but allow people to always have access to their backups" would be considerate.
Good luck :).