Hi, I will be happy to help you with your situation.
I don't think the mass is a reason to put your beloved "old man" to sleep. If the mass is not bleeding, infected or sore, then I would not worry about it at this point. Is it making walking or laying down difficult?
If he gets around ok then I would just let him be. If his arthritis bothers him, you can talk to your veterinarian about medication to help him get around better.
I feel like your dog could survive the surgery, if his physical exam and blood and urine values are normal, but his recovery time would probably be prolonged due to the size of the mass.
if you have any more questions, I will be happy to answer them
Feed back is appreciated.
It doesnt seem to cause him a problem when he lies down it just seems to move out of the way and i dont think he even know it is there he has never acknowledged it in any way i dont really want to put him through surgery he has had a very long good and peaceful life
Thank you for your help