After kidney tumour removal, they now suspect stray cancer cells have gone deeper into kidneys and bone marrow what are his chances, he is 69 my dad?

Oncologist. If there is a spread from the kidneys his oncologist will be the right person to discuss prognosis. Usually kidney cancer once removed has good long term prognosis is there was no evidence of metastasis.
Means. Bone metastasis , if that is true , he has advanced stage of cancer of kidney , long term out look is not good , speak to his oncologist , chemotherapy may benefit him.