Sorry that you had to go through that Mike.
My Grandpa is in a similar situation right now. Waiting for a big operation, but it's taking forever to get the final tests done before they can finalize the plan of attack for the operation (Aortic Aneurysm).
If I can only give you one peace of advice, is would be to spend as much time as you can with him, and like others said, just listen and chat. Even if it’s a weekly phone call, or quick visit. It can only help right.