broken residential lease we leased our house through 10/31/09.

broken residential lease
we leased our house through 10/31/09. the tenants gave us notice that they were declaring bankruptsy and vacating 9/15/08. we lost 6 weeks rent and had to pay a fee to a property manager for finding a new tenant. these expenses exceed the security deposit. can we keep the deposit?
what if we did not notify the tenants within 21 days?
thanks