That’s the problem I see...they asked about giving him a feeding tube. Is *that* the option? Let him starve? Don’t give him his insulin? It doesn’t appear that he’ll pass from this on his own and these options seem cruel. A type-1 diabetic requiring oxygen isn’t a great start for rehab to be successful - I don’t think he’s up to it, nor wants to be.
My mother was in exactly the same situation. She did not want to live life paralyzed, unable to speak and unable to move. The hospital gave her a feeding tube, but she kept pulling it out with her one good arm. If she were on insulin, she would not have wanted it.
She was so healthy, she survived her stroke and regained the ability to swallow, which is the key to eating and not choking to death.
All that did though was give her 8 months of decline, first at a nursing him, which was a bad experience, then at home, which was better. She had constant infections and agony. Our mother was a saintly woman, and I believe God was giving her one more trial and purgation, so that he could take her directly to heaven when she passed.
This is not in a good situation for you, and there are no good options. I am not at all for euthenasia, but watching my mother suffer, I also believe God does not that you go to extreme measures to prolong a life which would only be torture for your Father.