If you have some type of an emergency or hardship the landlord should be willing to make a deal with you regarding the security deposit.
Maybe if you agree to allow him to retain half of the deposit, and explain that you have an emergency situation, that might be enough to reach some type of an agreement. It wouldn't hurt to get another renter in there and simply sublet the space, but if you are in urgent need to move somewhere, explain the situation to your landlord. If you break a lease, you will need to, at the very least, show just cause or hardship if the landlord takes you to court. This does not mean you will be released from the obligations of the lease when and if it reaches this point, but if you have circumstances that are urgent, sometimes people are willing to make allowances- especially in the current economy.