I suggest you read up about how internet infrastructure works.
Even if Itch would lose their domain name completely from one day to the other, your things would not be gone. You would have just to wait the few days (or in this case hours) to reach Itch again.
Just like agaisnt ddos, as coincidentally also happened this week, you can't really protect against these type of srewups. Maybe the involved parties will update their tools and policies to avoid embarrassing scenarios like this in the future.
As for your archive, sadly, Itch is not a safe cloud space to store your purchases till you use them. There is always the possibility that the developer choses to remove the files. Look up what happened with Oxenfree this year. If you sell things here yourself, you know firsthand what is preventing you from removing files. (Nothing).