Wow your Dog is old! I think your Son is just upset because he will miss the dog & he is looking for someone to blame. He will be ok in a few days, and I'm sure in his heart he knows its for the best, he is probably just feeling sad!
It must be sad as you've had your dog for so long it must be like he is a part of the family, I've never had any pets, but I would like a dog I think!
"The Optimist sees the rose and not its thorns; the pessimist stares at the thorns, oblivious of the rose."
"Life isn't about waiting for the storm to pass, its about learning to dance in the rain"