Welcome to HCM.
I am Dr Anshul Varshney. I understand your concern.
See, no doubt he is serious and in critical state. But with your description i can make diagnosis that he is having:
1. Left MCA infarction
with Right side hemiparesis
2. Atrial Fibrillation
is the cause.
In such situation, if Afib is controlled, and he doesn't develop in other cardiac complication and infection, he can improve.
Usually death with these condition occurs due to Silent Ischemic Heart Attack
and also due to secondary infections due to bed ridden state.
If you could share with me about his general condition and his blood pressure, consciousness level and investigations, i can guide you better.
If you have any further query, please ask me.
Wish him a speedy recovery.