by most common and trade laws itch would not only have the right but a compelled requirement to distribute to customers who had purchased, however you appear to be right only because a badly worded agreement waived rights itch and customers should implicitly have:
https://itch.io/docs/legal/terms
has the very poorly done "If you choose to remove your content from the Service, this license shall terminate within a commercially reasonable time after you remove your content from the Service."
where the standard language for something like this would be:
"
- To the Company, a worldwide, non-exclusive, royalty-free, sublicensable, transferable, perpetual license to use, reproduce, distribute, prepare derivative works of, display, and perform the content in connection with the Service, including without limitation for promoting, redistributing in any and all media formats. If you choose to remove your content from the Service, this license shall terminate with respect to promotion and new sales; however the Company and Users who purchased the content shall retain a license to this content even after the content is removed from the Service for the purpose of fulfilling previously sold copies.
"
note i am not a lawyer, so you would need a real one to fine tune it