I just read through the entire thread.. Interesting read. I'm glad to hear the fishy is on the mend and doing better.
Had that been my fish, I would have done the same as the op. Many of my fish came to me in bad shape, and in time they have grown or are growing into beautiful pets. There is definitely a "collectible" side to fishkeeping, but in the end, fish are living creatures whether they are damaged or not.
If they are suffering to the point where they have given up, then I would euthanize, and I have done so in the past.
Sure, I like fancy fish. But I am in the end more fond of giving an otherwise doomed creature a better life.
Way to go op!