I can’t answer for sure, but I know from lots of experience holding off on ordering things and then having them go out of stock they rarely come back in stock! Then of course I kick myself for not ordering! This is all
shopDisney.com, not the shop Disney parks app, I’m not sure about that. I do know that I have seen a few things come back though, so if it isn’t any kind of limited release or special item, or a sale item,but one they intend to continue carrying, there is hope!
For example, I know the dress shop dresses have shown out of stock and then have been restocked. But when a bathing suit size or one size of one of the matching family shirts go out of stock I have never seen them restocked.
I know it isn’t ideal, but sometimes you can find things on eBay that aren’t marked up ridiculously and are prices i’ve been willing to pay.