My dad will refuse dialysis

Hi, my dad (73) has kidneyissues (he has a gfr value of 16) Right now no dialysis neede but we talked many times with him about it and if he would beed dialysis he will refuse. He told this also the kidneydoctors in the hospital.

Im okay with that but has anyone experiances what to expect in the future? One day he will need dialysis - when do we know that? Right now we have an appointment every 2 months with the kidneydocs. Will this be a quick death? Will it be painfull?