Earlier we had Storm Worm , now we have Mega-D and other botnets.

Botnet herders keep on moving to new botnets all the time (call it evolution), so i don't think being in limelight effectively killed any of these botnets.

Also the botnet tracking mechanism works only for a limited time, e.g. storm worm has changed multiple times. So what you may think as a sign of weakening after the limelight; could be just that botnet herder reprogrammed the c&c mechanism to avoid detection.