They get a private download url that can be used to download the latest version of the game whenever they want.
Another question occurs to me; Do you have a policy regarding early access to games? I saw you mention it on your twitter but your FAQ doesn't set out a requirement for games to be feature complete.
I'm very close to deploying a feature for registered users to view their purchases. I'm doing a revamp of user profiles and that's part of it.
Early access games are interesting, I think it's a realistic alternative to kickstarter. I don't have any rules regarding them, still thinking about it, but I very much encourage them.
Thank you for itch, it's a great service and I hope I can use it in the future.