Usually when the battery fails or falls out of an electric car the car would kind of stop by itself. No juice no go. Which is why failsafes are not used in electrics. As far as interference or out of range issues are concerned, most if not are ESCs stop sending current to the motor. BTW some very old mechanical speed controls (wiper style operated by a servo) could benefit from a failsafe and TRS.

With nitros the failsafe will not do anything if the receiver pack fails. The only solution is a TRS as stated by DaveH.