This is only a wild idea and i wonder if this can be a workaround the fact that s2Member does not offer a notification to the members that their membership is about to expire.
I can imagine that i have a product that gives access for 3 months to certain content. After 2 months and 2 weeks, one chunk of text can appear on the special access page saying "This is a reminder that your membership will expire in 2 weeks", and then, another one, one week later displaying "This is a reminder that your membership will expire in 1 week", and finally one saying "This is a reminder that your membership will expire tomorrow. If you want to keep access to this page/content/etc. please click here (and that would be another button)". Would that work?
Now, with the conditionals and the dripping content, would it be possible that this would trigger sending an automatic email, a bit like the Thank you email sent by WP? and it could be timed, again, 2 weeks before expiry, and one week and one day, etc.?
(disclaimer: i am NOT a coder, just a dreamer)