People are gonna be pissed either they rollback the servers or not. There's no win-win situation here. K2 is fucked either way.
They prolly gonna make the people who lost their items through the merchant hack happy, but will piss off people that upgraded/traded/bought/exp'd/farmed stuff too.
I wouldn't like to work at K2's Customer Support atm and be reminded of my mother in each ticket ._.