I would suggest that waiting it out would be identical to just flushing the guy right now... i.e. no chance of him somehow overcoming the infection and recovering without treatment. Mine was fine for about 6 weeks before he came down with it, as I recall. That indicated to me that I was somehow stressing the fellow, not providing the correct nutrition, or both.
I would pull him to a hospital tank, and research which treatment to use. I'm sorry I can't make a hard determination for you on the medication. I tried Erythromycin, but the little bugger went for a walk before I could determine how effective it was.
I had also done a fresh water dip (pH and temp adjusted) for ten minutes, and was using Stop-Parasite. I figured I had one chance to save him, so tried to cover all the bases.
Good luck, and please keep us informed.
Zepha