On the other hand you are not purchasing storage space either. I think as long as you were reasonably able to download the things you paid for, then Itch has fulfilled their end of the bargain.
Think of it this way, if you paid for something at a physical store and then forgot to bring it home, you should be able to go back and get it within a reasonable time frame. But if the store closes down 6 months from now and you still haven't retrieved your item, it's really your own fault and it is unlikely that you will get your item even with court involvement.
Similarly, you cannot expect Itch servers to exist forever. You should be downloading things as you purchase them and preserving them on your own hard drives which you can easily have multiples of for security.
This is a case by case decision, but I believe if a developer sells anything and does not give an apropriate grace period to download it, Itch would see that as grounds for a refund request.
There is more of this in the tos. But basically, your rights as in licenses and such to use the software are unrevokable. But there is this kinda loophole, that neither Itch grants it's continued existence nor the developer is required to keep the files on Itch indefinetly. It has happened lots of times with all those cloud services where you could buy digital files - and not even download them. It is quite an outrage and #1 argument against drm. Coincidentally, drm is frowned upon on Itch and I have seen such very, very rarely.
