Sorry to hear that, 90% of the time they never recover from dropsy even with medication so dont feel too bad. Its one of those diseases that stick and do massive amounts of damage until the fish is dead. That seems like a very ruthless case of dropsy, you did what you could so cheer up! After 30 full grown platies died I gave up on breeding fish and learned to quarantine fish especially from petco/petsmart, in your case it looked like it was water quality so stay on those weekly w/c's! I got one platy that had raised scales from petsmart and within a month everyone was dead but the fry, I was pissed lol. But cheer up, its rarely a successful story about dropsy.