We do have a quail section, Sooz, and having kept both chickens and quails, I think there are enormous differences between them, apart from the basic physiological similarities that all birds share. The problem with all birds being kept domestically is that their metabolism and internal structures are so different from mammals, and they are so much smaller, especially quails, that there has been little research done on how to treat any but the most common problems. Vets are often under-informed and tend to just hand out antibiotics on the off chance they might do some good, or to try remedies such as surgery which are not only risky to a bird with totally different breathing arrangements from mammals, but incredibly expensive for most of us.
People do differ on where they draw the line when a bird appears to be suffering with a serious illness, and i know many of us go to enormous lengths to help a pet bird hang on in there - and sometimes, at least in chickens, this does appear to work, for a while, depending on the nature of the problem. I do agree with Mrs B. that supplements are unlikely to help an illness such as ascites, which as I said, suggests other internal problems unrelated to inadequate diet.
Nobody will be critical whatever course of action you take with you little quail - but those of us who have been faced with similar dilemmas over the years often feel that a swift and humane end can often avoid a long and possibly painful struggle which will eventually result in death anyway, and we can only advise from our own experience. It's up to you, what you decide, and we'll be very interested to hear what happens.