What happens when contract is making delegatecall to deleted contract?

Question

I read the whole Suicide Parity Multi-sig hack. One thing I don't understand is what happens when you call delegate call on deleted contract? I thought that contract should throw an exception but due to the attack description it doesn't. Why this code returned true?

function isOwner(address _addr) constant returns (bool) {
   return _walletLibrary.delegatecall(msg.data);
}