I have just read your post and really broke me heart...
I could not make such a big decision without knowing i had exhausted every possible avenue, i would do anything for my dogs and if the vet was insistant that there was nothing they could do and the dog was in pain i would not hesitate as painful as it was. I have lost 3 dogs in total to ill health all at good ages thank goodness and i know how pain staking it is. I still get upset over lost dogs because they have bought be so much joy. SO much so my current dalmation she is only 2 in april, but her mum had a massive heart attack at 5 years old and i am frightened.
one of my last dogs...Penny was found to have cancer and only 6 months to live which gutted me, btu she lived 2 and half years longer.... but you know your own dog hun...dont give up thats my advice.
Basically i am saying i would do anything for my two girls (my dogS)!! they are part of the family... i just hope bailey gets better soon for you all at such a young age.