Will a servo hold its position without a signal?
It is very doubtful that it would stay in the same location.
The way I understand servo motors to work is that there is a constant feedback loop that is comparing the position to your pulse. Something like this:

To explain a bit more, the pulse is feed into what I called a low pass filter. It turns your pulse into a voltage that is in the range that the position sensor should also be outputting. It is also designed so that the voltage is maintained during your pulses 20ish ms off time. This voltage is then compared to the position sensor output. If they are equal then the motor doesn't need to run, but if they are different then the motor will run forward or backward to attempt to make the error be 0.
Now this is a very simplistic way of looking at a servo as most have more complicated control systems to insure stability with fast response, low overshoot, and high position accuracy.
There is a chance that there are servos out there that have &quot;memory&quot; of the last pulse so you don't have to keep sending it a pulse train, but none of the ones I have used do this.