Your contract will state that you have to give at least one months notice to the landlord when you want to move out. If they haven't told the landlord (if they're that sneaky they may have) then they lose their bond. Presumably you all chipped in equal amounts when you moved in? As jug suggests, approach the landlord, explain the situation and ask that the girls share of the bond be used to finance the rent. He/she may even be able to help you out with a slightly reduced rent. You won't lose anything by asking. And of course, you'll need to be very pro-active in finding people to replace them.