The sub firmly believes that no answer is ever final, so more insight is always welcome on the matter for anyone knowledgeable to fill in. In the meantime, here's some previous posts on the matter of comatose care before modern medicine:

• A now-deleted user offers the medical side of things in this thread;
• u/jpallan offers insight on Henry VI in this thread.
• And bonus: u/itsallfolklore has a post on how the comatose were socially regarded; not directly medical, but related and interesting.