The mortgage is one of the assets seized by the FDIC and sold off to meet bank liabilities. On your end little should change in the short term, and you may have a different owner for the mortgage at some point (and as I understand it, your mortgage changing ownership is a fairly common occurrence in general). As far as payment and servicing goes, there should be continuity in how that is handled.

In short, you'll still owe somebody, it just won't be a bank that doesn't exist anymore. Over the short run, the FDIC or an acquiring bank will take over the back-end of the payments, which will be made much the same way as they are today.