Ricki hugs to you, I can't imagine how difficult all of this is for you. It's hard to love someone so much you want to let them go for their own sake. I have had similair experiences with my grandpa, and just recently with my grandma.
In the days before my grandpa died, he really came around he was joking and teasing like he always had. Up until then he had been in and out of sleep and not really responsive. He got to see and talk to all of the family. It was the next day that he passed on. It was like he came around to say goodbye to us all. Right before he died he reached up his hand my grandma says and said the name of my great uncle that had passed before him. With that he was gone. :\\\'(
My grandma had been in the nursing home and had been ill on and off for months. The nursing home staff told us she was basically shutting down. She ended up in the hospital and within a day they were calling the family in and she requested the minister come read her last rites. The nurses said she was going soon, her vitals were consistent with someone that was dying and the family was there to say goodbye. Funny thing though, my grandma always did things on her own terms. By the time the minister had been woke up and arrived at the hospital, she had come around. Grandma was sitting up and kept interupting the last rites and joking with the minister. The next day she was 100% better!? They kept her one more day in the hospital, then sent her back to the nursing home! It was odd though, grandma was talking to me and kept telling me she was going back there for "three days and that's it". Well, she did. She went back to the nursing home on a Wednesday and was never the same again. That Friday she slipped into a coma and was gone. She never made it through that third day. :\\\'(
It was terrible to go through all of this, but I think people do tend to "get better" in the end and I think that is so the family can have that memory again of the way the person once was. I think some people also hang on waiting to say goodbye. My grandma knew my Mom was coming from California to visit, and at one point had told my aunt "she better hurry up". My heart goes out to you and your family Ricki. I hope your grandma can find peace and comfort.