The rent-to-buy option can be exercised only with the owner of the home. Using the funds credited to you under such an agreement has to also meet lender requirements (e.g., specific terms in written lease, only portion of rent above market value is allowed) so more often than not it would have been better to simply put the money in a savings account. If you're not planning on financing then whatever you and the landlord agree to would be just fine, otherwise your agreement is only as good as your lender allows.
If the home is really foreclosed then your former landlord no longer owns it - you'll need to negotiate any rent with the new owner, the bank that held your former landlord's mortgage. If the bank agrees to this at all this would be short term at best because, as the others have pointed out, the bank wants to sell the home and not be a landlord.
Since you wanted to buy, your best option is to speak with a mortgage professional who can do business where you're looking to purchase (I'm able to finance in all 50 states.) Depending on the area and circumstances you may qualify for a 0% to 3.5% down payment and the seller may contribute toward your closing costs.
If you really want to continue to rent rather than purchase right now I would suggest looking for a different place right now.
I'm sorry if that's not what you wanted to hear. It's unfortunate that your plans had changed due to your landlord's situation but let's move on and see what works best for you now.