What kind of behavior do does have when passing?

I have yorkie, male. He is around 12 so he is aging up there. We took him to the vet a few months ago only to find out he has congestive heart failure. He has been getting his medicine daily, but the vet said since he is old h may not last long, she also said if he were to pass it would be pain free. He has been sleeping a lot today and can hardly walk, I also have a female yorkie and she has been laying with him a lot more than usual today. Is it possible that he might be passing away? If so, do you think he will make it threw the night?