Can the US even afford a war?
Under the law, the debt ceiling will be set on May 19, 2013 to a level "necessary to fund commitment incurred by the Federal Government that required payment."
I don't believe that covers new commitments such as war.
If the north Koreans do Infact stick to what they're saying and bomb America, I don't think they'll just sit tight. Especially if they somehow drop a nuclear bomb, America will retaliate tenfold. They always have done.