When my mom got cancer, 1989.. she had every reason to fight. She had children she adored, married to a man who worshipped her, paid off house, so she fought like hell. Took rounds of chemo, got an implant to house a needle for a lifetime without getting necrosis..yada yada.
When my grandmother.. who watched my mom's battle, got cancer.. like 1993.. she refused any treatment. She had nothing to fight for, asshole granddaughters (my sis and I) and a son she hadn't talked to for decades.
I have a friend, a little older than I, came down cancer..John knows him..he plans to refuse treatment. He's seen how this usually goes, and has no interest but.. he also has no kids, wife, career.. I'm dying, myself.
I quit smoking, I pulled back on drinking.. {What killed my folks} Not for me, but for my kids. They didn't ask for that, like my sister and I didn't want it. Sadly (?) I came down with MS. First in my family. I am fighting, for the kids. They need me like I needed my mom, but smoking took precedence. I chose to bring them here, it was my fault. I owe it to them to not check out without a war.
I wish for your grandpa the best quality of life possible for as long as he wants it. *hugs* Find peace with it.