They can still torrent the content, which is what I'm doing after I paid for the first month of Disney+ and then found out their DRM disallowed Linux because of "security levels".
The stream quality of HBO GO is consistently bad on Linux, with washed out colors.
I have no experience with Amazon Prime Video, but I've found several threads from 2019 with people complaining about the lack of 1080p streaming on Linux.
So even when Disney+ begins supporting Linux, you'll most likely get a subpar service for your money.
It sounds like Disney+ was accepting refunds for preorders up until the launch day. Whether or not they can refund after presumably may depend on whether or not they can tell you've watched some of the content.
Personally I view is as a moral imperative to not give them any money.