How Long Can A Person Be In Diabetic Coma?

My Dad has gone into a diabetic coma, luckily, he was transported to hospital after he wouldn t wake up. He is now in a ward and is on a glucose, antibiotics drip ect... He has been unconscious for around 48 hours, maybe more. When he is spoken to, he is responsive and grunts and groans. He is breathing on his own too. Will he wake up? And roughly how long can one remain unconscious? Many thanks.