I really wouldn't write him off just yet. Treat him and see how he does. 99% of the people I mentioned it to told me that one of my bettas who was suffering from dropsy was most likely going to die but I got him some Maracyn-Two and treated him with that anyway, just to give him a chance, and a week later he's completely cured.
Really, it's up to you, do what you feel is best for the fish, but I would definitely consider medication if I were you...then at least if he still doesn't make it you'll always know that you did your absolute best.
I hope everything works out...let us know!