If the receive gets a corrupt data packet (i.e. detects interference), it will respond by simply holding the last servo position.
If the signal interruption persists, then it goes into fail safe. The delay isn't very long. I think just a second, or so.
What happens when it goes into failsafe depends on how you set things up.

The one plane I have with a PCM receiver is setup to idle the engine, and give full rudder/elevator/aileron deflection. As such, it will slow down quickly and spin to the ground in very short order. Hopefully out of harms way. It also lowers the gear - so that it will be abundantly clear what happened.