I think it's a little more complicated than that. In a 50 First Dates type of scenario, their ability to form certain types of memories is damaged, not non-existent. And I would argue that with enough brain damage someone like an extreme lobotomy victim may stop being considered conscious.
I’m not familiar with 50 First Dates, I was thinking of cases like Clive Wearing [0]. I would agree that consciousness requires some sort of ultra-short-term working memory, but I also think that mechanisms similar to CoT loops can conceivably fulfill that role. Today’s generative AIs consist of more than just the static network-of-weights model.
"Wearing can learn new procedures and even a few facts, not from episodic memory or encoding, but by acquiring new procedural memories through repetition. For example, having watched a certain video recording multiple times on successive days, he never had any memory of ever seeing the video or knowing the content, but he was able to anticipate certain parts of the content without remembering how he learned them."
Honestly, that's a pretty messy state of consciousness and I wouldn't proudly crow that my AI is conscious if that's as good as it got