There are alarms for everything under the sun, I don't think it would be possible for a fire to knock off a key system and the pilots not know about it.

In the world of Electrical Engineering ANYTHING can be knocked off without you knowing, because at some stage you just HAVE to assume that given circuitry works. With radio comms, the only way to check if antenna is actually working (a connector is still intact) is to use receiver. That's what commercial radio operators do