pro sites – lifetime subscription

Hi, thanks for taking a sec.

I’m looking to add prosites to my mu install.

I’d like to be able to create a coupon that gives lifetime access.

Whats the best way to achieve this.

Or do I need to renew them each year?

If so, will there content still be live once they re-add the coupon?

I’d like to keep it as simple as possible and also be sure that their content/sites will not be deleted or lose any of the content they’ve posted.

Thanks so much for your help & patience,