A couple of things, renewal is optional and not required for you to continue using the style. If you don't renew, you simply will not receive updates or support on the forum but you're entitled to use the style still.
You can still use the style indefinitely assuming it's never revoked. The license could be revoked for various reasons such as redistributing the style, using on more forums than you're allowed (one live one test site) or other things outlined in the license agreement. Although this hasn't really been an issue since we've been open .
The support that Russ and Steve offer is priceless. The cost of renewal is very affordable and well worth the extra mile they go to help out their customers. Even questions that some places would be like "nope that's custom work", they are happy to help out with.
I'll even be considering adding the Remove Branding Option in the future, whilst still keeping a link to their site.