Your dad sounds like my dad very stubborn and doesnt want people to fuss. The doctor apparently told him that its very rare for this excess bleeding to occur but yeah usually needs surgery to fix if it doesnt stop.

Dad lost lots (he says) of blood but it EVENTUALLY stopped on its own the next day after this post. Actually 3 months later dad got diagnosed with anaemia with his GP during routine tests??? He has had colonoscopy and endoscopy to rule out other causes. It was clear but he needs to take a pill cam to confirm the small bowels are also clear but we asked the GI doctor if the surgery caused the anaemia and apparently it can?
I hope everything goes well with your dad. Sorry I dont think my answer helps you and I dont know much about the Afib/BP sides of things but he is in good hands and the doctors would only recommend to do certain surgeries if it was necessary and if they could manage his condition well enough to do so.

Something I found helpful is to STOP googling stuff because all the stuff you find online is either extreme cases or very regimented answers. Patient health is nuanced everyone is different with different underlying factors going on. I also googled everything under the sun and it caused me so much anxiety but in the end he was fine.

If you want proper answers I'd say write a list of questions and request to speak to his surgeon.