Bill,
We always hear that dogs are man's best friend. Until you are faced with losing one of your own, you never really understand that.
I feel for you and comend you for taking in strays. My wife and I have done the same (we have 2 dogs). Both are around 10 years old and in fair health.
The thought of losing either one of them is tough. They are always there for us, they never judge us and they are ALWAYS happy when you come home. To them, you can do no wrong.
When that level of commitment and joy is taken away from you, no matter how old the dog was, no matter how many people say 16 years is a long run, it hurts.
Really sorry to hear about the lose of YOUR best friend.
Take care,
Charlie