Yes, and reverse all transactions that took place during the 51% attack.

The attacker sends coins to an exchange, waits for 6 confirmations, then reverses the transaction.  The coins are now back in the attackers wallet but reflected in the attackers account on the exchange as well because of the way they are set up.

Now he has those coins in his wallet AND on the exchange.  He can keep repeating this until he has accrued millions of coins on the exchange, then sell the coin down to 0.00000.