I hope someone helps with the specific question. I just have a thought for you.
I use subscriptions via PayPal, and setup monthly subscriptions on PayPal that my members can subscribe to via XenForo. There are various prices/options they can choose. The advantage of doing this is that their subscriptions never end.. which seems a more normal/logical idea than something that constantly has to be resold/rebought and that entails the sort of problems you are trying to work around.
The way I do it I consider to be simply the normal way to handle a subscription... and the same as say Sky TV, AOL, or most other things you might subscribe to. They will all be taking a regular monthly sub, none will normally be saying you can't use them because your subscription somehow expired... why would any business do that to its customers etc.
I suspect it would help a lot with member retention rates as well as meaning no problems of the type you are dealing with. A small monthly amount a member can cancel whenever they want via PayPal is also a much smaller hurdle for them to jump to start a membership in the first place when compared with an annual amount. There are lots of other plus points for working that way...things like being able to close down a system owing nobody anything, and all sorts of other subtle stuff such as where people decide to leave subs running even though they may not use the system for some years etc.
Just some thoughts, hope they help, if not please just ignore them.
Steve
