Looking for answers

My  husband is 81 he has untreated stage one bowel cancer  also mid stage dementia. He had no energy and sleeps most of the day . I know he can’t be operated on but how long can he survive  I read so much on the web but it’s confusing and refers mostly to treated cancers giving such a short time to untreated people , ther is so much he wants to do have I time to grant most or all of them