The idea that an exchange can rollback a cryptocoin "blockchain" is very damaging to the confidence -- that's not something anyone should fiddle with.
An exchange can't rollback anything in NXT. Only forgers can attempt to do that, if they amass 51% of forging power to create a longer chain. Same is true for any other coin. In the future, when Transparent Forging is implemented, forgers would have to amass 90% of forging power to be able to rewrite history. Judging by reaction of forgers to today's incident, this is not gonna happen, ever. Most forgers are for irreversability of transactions, which is one of the main ideas of crypto currencies.