@Helping_hand_ - When is your Dad's next appointment with his vascular team? If you feel you are not getting through to him, then in your shoes, my next steps would be to approach his vascular team; not for a consultation, as they may not agree to that, unless your Dad had consented to his condition being discussed with you, during his acute phase.
Again, I would write to them, expressing my concerns about his diet, and smoking aspirations, suggesting his preference appears to be to revert to his pre-crisis lifestyle . Hopefully they would take the time to reiterate the need to change to look after his diabetes and for his vascular health. I have a strong suspicion that the re-plumbing job he has had done on his legs would be a far bigger challenge to do again, if it is possible at all (I have no idea). Perhaps the prospect of a re-run of the discomfort, fear and loss of independence could be helpful, bearing in mind how fresh all of that is in his mind at the moment.
The reason my Mother's toe/foot/leg was saves was she won the lottery, in terms of luck. The tiny clot blocking the blood vessels she had left to her foot resolved spontaneously. Apparently that in incredibly rare,a dn the vascular surgeon was at enormous pains to stress to my mother that the chances of getting that luck another time were minuscule.
Good luck with it all. I do hope he catches on before you strangle him! You really are trying hard.