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.

They are conscious because even for short periods of time they do form memories and those change them even if only briefly. They think on their own too. It is a very limited level of consciousness though.

I was like this for a bit and you still have memories from like 30 seconds to minutes ago, but after that you have a cliff where you don't remember.

I don't think LLMs structurally even get the 30 seconds part. It's literally 0 for them.

Interesting point but even those people’s brains aren’t immutable. The have habit change without memory.

they still have memory, just not new ones - they lived experiences

vast oversimplification of the experience of brain damage

Someone getting in an accident that chops their leg off doesn’t mean humans don’t have legs. Come on man.