Bless his heart....
I don't really know what to say except if you feel he can be treated....then treat him ......Pnemonia
can be treated.... and while it may cost you more in vet bills ..this is the responsiblilty we take on when we get a pet.....
Good luck and I hope he gets to feeling better....personally...I couldn't let go if UNLESS the dog was was suffering and untreatable.