I am truly sorry and know exactly how you feel. My Dad was diagnosed with a MM at the age of 81 and passed away two years later. He had let a large black mole on his back go for a very long time. He had a large excision but of course the MM had already progressed to his blood stream and so to all parts of his body. He wouldn't go for any treatments and lived well for almost two years, even then refusing doctors and hospitals until a month before he died. He chose Home Hospice and died peacefully at home.
I will keep your Dad in my prayers, and you too. Older people very often get a type of melanoma called "Lentigo Melanoma" that spreads on the surface of the skin for a long time and is also highly curable. Sometimes you see it on the faces of the elderly, large dark patches. Please post and let us know how your Dad is doing. My Dad wasn't concerned at all despite what the doctors told him because he "didn't believe in skin cancer", it's just somthing doctors made up to get money from people.