I'm pretty certain that "drop" is not the case here, more of an injury thing. Rohit is too big of a player in the ODI side to be dropped.Both if he is dropped from the white ball format then Indian Cricket is just doomed for the bad.
Regarding "if he is not fit then why he is gearing up for a return in IPL", best guess would be the $$$ factor. Owners might have arm twisted BCCI into letting him play the remaining matches as he is an integral cog in MI batting as well. I wouldn't rule that theory out.