Let me add a caveat to getting out of a lease. Just because the landlord is not paying the mortgage, it doesn't mean you don't have to pay rent or can just break the lease without cause. These are two separate contracts.
I have seen landlords take renters to small claims court and consistantly win when it comes to getting rent money. Look over your lease carefully before withholding rent or leaving. Now, the landlord may be fine and let you out of the lease but that is their decision. And I would get any agreement in writing.