"not require hospitalization"We'll probably never know (and honestly it's none of our business), but I'll always be curious about what happened between Tuesday and Thursday that resulted in such a sharp decline but did not require hospitalization. I suspect she either died suddenly and the earlier statement was just to give us all time to prepare, or else she had a terminal illness that they were managing quietly.
Maybe she wanted to die peacefully and at home and she refused hospitalization when in a critically condition? My father had made a patient's provision, in case he wasn't able to make his own decisions anymore. I could imagine that the Queen was the kind of person who wanted to have full control over this last chapter in her life. Today's medicine can keep you alive for a long time, even when you're in coma with few hope that you gain back consciousness. Imagine what this means in the Queen's case? Instability of the monarchy.

There's only one Charles around.