Hello and welcome Muse
I can certainly sympathize with your dilemma, but the one who makes the decsions on this ........is your Dad. As much as we are distressed with ones like this, it cannot be changed.
Delicate operations with great risks do not always turn out badly. Try not to eat yourself up over this because it is out of your control. Your Dad really feels that he is conducting his life and choices in it---according to what God wants of him. That's a pretty powerful force to reckon with, Sweetie.
Look into the options that the posters here have mentioned to you, and then let go of it. Place it in God's hands from there.
hugs,
Annie