The MultiWii FailSafe will try to save your copter and environment by slowly descending and (after a configured timespan) engine shutoff if the radio signal is lost.
Failsafe with FrSky receivers
The documentation for the FrSky receivers tells us that rebinding the receiver will disable failsafe. The receiver will continue to transmit the last received value, however so the flight control can't detect it. If you have a FrSky receiver, in order to completely disable the failsafe built into the receiver, you need to push the button on the receiver while the transmitter is turned off.