Hate to hear that. I too have recently lost my Grandpa back in early December. It was tough on me, but obviously tougher on my Grandma. I call her everyday at 6pm. If she doesnt answer on the first try, I try again. I have seen her go up and down, both mentally and physically the past few months. Hard to see, but I think she is getting some will to live in her again.
Remember the good times you had with him, and be there for your wife because she will need it. Times like these are when we have to live up to the for better or for worse of that agreement we made. Even when it hurts and is hard to do, you will have to be strong for your wife.