Delete please

This isn't possible I think, and I'm surprised you have considered it as an option - the addons are provided in a download file which are extracted onto the computer's LOCAL machine, local game installation directory. They are simply text and graphic files, albeit written in Blizzard's LUA scripting language.. it's as uncontrollable as, e.g., providing users with a list of available Wordpress themes which you then want to stop from working if they unsubscribe. It isn't going to happen due to the nature of the product distribution.

Add to that that it's probably against the TOS, Blizzard have already cracked down on donate buttons in any third party addons... they would come down on you like a tonne of bricks if they found an ongoing subscription service that (somehow) found a way to cease the addons working if a user cancelled. Blizzard are notoriously hardline about anything dodgey or which might annoy its users. They already have lawsuits ongoing against a number of parties, and whilst I'm not saying they would do anything as drastic as that, they DO have a reputation of "ban your account first, ask questions a few weeks later, often hitting a brick wall with customer services". Trust me, I had a friend who had an account banned for several weeks due to "account sharing violations" before she could prove that their procedure to identify such a thing had totally screwed up, she was totally innocent (and baffled) and the customer service reps were incredibly unhelpful all around (her (minor, acceptable in the terms to share with) son had logged into her account from the USA whilst staying with his grandparents on a holiday, they saw the ip from two different continents, auto banned it within a moment).

Thirdly, I'd be suprised if you could even get the clients to pay for such a thing due to the demographic of the game ;p

.... on a slightly more positive note, you COULD look at it from the angle that the content patches render ongoing maintenance of a user's addons a requirement... the moment a new patch hits those addons are at LEAST placed as Out of Date and have to be manually re-enabled... not to mention the API changes the published makes between content patches..

So, in summary, you basically HAVE an in-built method to prevent old users from benefiting from your work. It's from the angle that they won't get updates any more, sure, but it would work for most users, most technically competant users might fiddle around with trying to fix errors appearing in the addon due to it being out of date but I suspect the tolerance threshold would be low... and that is a tiny percent of the playerbase even getting that far.

I'm surprised you considered this since you're thinking of providing the service though - I suspect you need more knowledge of the game/target market before you actually do this further. It's not meant as an insult, and I wish you the best of luck, but it is a rather odd question to post

Ah I see, that makes sense then

Don't be discouraged by my first few paragraphs, btw, I just read my post and it seems all doom and gloom lol.... but that self-policing patch content stuff would really do the job you're asking quite passively for you (albeit not totally securely!).

Depending how you do things, yes, you can 'disable' information after a subscription has expired.

As for the WoW, I haven't taken a look at what their programming language looks like. But with most computer languages, of course it is possible to do that as well. Only 1 thing -- if the WoW language is not encrypted/compiled/etc, it is pretty much trivial for someone to 'reverse' that and remove any form of copyprotection you implement.

Since WOW has Cataclysm coming up, you could make them pay for your add-ons each time you update them?