Thanks for all of your replies. Probably I am not explaining this well. I think I understand the current functionality (thanks for the link anyway). What I am looking for is extended functionality (a feature request).
I am going to start over and give examples based on my original posting. For the sake of discussion, assume that the Subcribe2 settings have new users registering automatically be subscribed for e-mail notifications. Also assume many registered subscribers (WP users) and many public subscribers.
1) The administrator deletes a registered WP user for writing posts, etc., but still wants them to receive e-mail notifications without having to manually enter them as public subscribers. The users must be able to unsubscribe themselves for e-mail notifications.
2) The user decides they do not want to receive e-mail notifications, but still wants to remain as registered WP user for writing posts, etc. The users must be able to unsubscribe themselves for e-mail notifications.
I think the easiest way to accomplish both of these scenario's is to give all registered subscribers (WP users) a public subscription, perhaps one that also allows HTML notifications, that users can control independently of their WP user registration.
This would be in accordance to Directive 2009/136/EC of the European Parliament (http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2009:337:FULL:EN:PDF)
2. Notwithstanding paragraph 1, where a natural or legalperson obtains from its customers their electronic contact details for electronic mail, in the context of the sale of a product or a service, in accordance with Directive 95/46/EC, the same natural or legal person may use these electronic contact details for direct marketing of its own similar productsor services provided that customers clearly and distinctly are given the opportunity to object, free of charge and in an easy manner, to such use of electronic contact details at the timeof their collection and on the occasion of each message incase the customer has not initially refused such use.