These sound all nice and friendly, but they're not feasible for me. If you've paid me, use the service for a time, then ask me to delete all data associated with your account, I've got nothing to fight a chargeback with. Shutting down after losing a patent (or other) lawsuit, then open sourcing the aplicable software seems wrought of peril. 6 months notice is feasible for a paid service, but not so much for a free on…
You may not even have that option:
http://www.dataprotection.eu/pmwiki/pmwiki.php?n=Main.HU
As for keeping the history for anti-chargeback purposes, it is my understanding that you are allowed to keep username and log in data and your IPSP will have the rest of the information that you'd need to fight a chargeback.
Also, someone requesting deletion of their data would make it pretty easy to fight that chargeback because they're providing you with auxiliary proof (the request itself) that they've been active users of your site.
The patent claim is a good one, I'll have to think about that.
Keeping a free service 'up' without allowing new data to be entered in to the system post shutdown without support or development costs a very small fraction of what it would cost to run the service in an active way.
For example, Yahoo! claimed that running Geocities cost them tens of millions of dollars annually, and yet, somehow I can maintain a large fraction (how large a fraction we'll never know) of their accounts up and running for approximately $500 / month.
The problem with giving notice is that many people will never get your notice, even when given 6 months ahead of time.
Imagine dropbox shutting down their free accounts overnight. It's technically within their rights. Ditto google docs and a myriad of other services that people come to rely on.