In this unlikely and rare event, not much will change. The full balance of your mortgage won’t become due immediately.
Your mortgage won't be wiped out either, you won’t be foreclosed on, and the mortgage rate wouldn’t drop to zero.
In fact, you may be surprised to find out that the originating bank or lender (the one that agreed offer your a mortgage) doesn’t even hold your mortgage anymore; it could have been sold off to another loan servicer years ago who has been collecting payments from you ever since, in which case nothing would change.
If the originating bank still held your mortgage at the time of failure, you would receive documentation from the new owner with instructions on how to manage it going forward. The end result would be sending that monthly payment to a new address and having to setup your payment details with the new bank.