There is nothing wrong with walking away on this one. I disagree with Rustico and sdrealtor. You did not enter into an investment relationship with the bank so the comment about shared profit is rediculous. The bank agreed to lend you money with the condo as collateral in exchange for interest paid by you. If you stop paying they get the condo back, they are not getting a raw deal, just the deal the outlined in the agreement( one that had multiple possible endings that the bank is fully aware of ). Sure it wouldn’t be the ending that the bank imagined or that you imagined. Life is full of twists. But it is obviously an ending that was outlined in the agreement, up front.
I suggest you do what is in your best interest. I know that is not easy to figure out sometimes, but don’t be fooled into thinking you would be doing something immoral by handing in the keys.