First of all, you should be able to maintain a signal as long as you can see the airplane. If you loose the signal, shutting down the motor is really the last of your worries. You need to have control of the airplane and without the signal, you have none.

As for the pre-set servo functions, the higher end transmitters do have a thing called "failsafe" mode. This "IS" when the receiver looses the signal from the transmitter, the servos go into a pre-set position. Most people, when experiencing want to have the engine go to idle. As for the settings of the surface controls, some want them at neutral while others want a little up elevator and a little bit of aileron to make somewhat a turn should you loose the signal. As far as I'm concerned, I like to have the throttle at an idle and all the surfaces at the last know position before the signal loss. I'd rather not try to figure out a new starting point once the signal is regained.

Now, that all depends at what attitude and altitude you're at when you loose that signal. Anyway, a novel could probably be written about failsafe and it's advantages/disadvantages, but to answer your question, you'd be looking for a radio system with failsafe to provide you with a change in throttle setting when the signal is lost..