Well, here is my reasoning why Kuro might well come back: I do feel that the story could have ended perfectly with Shirou dying after sending off Miyu, and Miyu staying in Illyaverse forever as a result. However, they had to prolong the series longer and longer (AFAIK in the commentaries of the first tankoubun, Hiroyama Hiroshi mentioned that the original idea was to finish the entire story in one season) and change the story in such a way that Shirou somehow is still alive after all that. Therefore, it wouldn't surprise me at all if Kuro comes back. I mean Shirou sustained a direct hit from AE of Gilgamesh lmao. Surely that was much more serious damage than Kuro losing her Archer card? Maybe she'll be reincarnated in another form. Let's see.