when the engine dies out, is there alot of fuel in the tank?
Motors wont restart easily if there is very little fuel in the tank. If it happens when the tank is half full or so, then your needles are not balanced and your engine is out of tune. Regardless of how much fuel is in the tank, a motor should just start right up, unless the temp is really high like above 270.
your servo problem reminds me of a problem I had. Yes if the middle gear is stripped, the motor will keep moving. If the servo is still under warranty, send it in. If you are not good with repairing servos, find someone who his help you out, you have to make sure the gears are lined up properly in order for it to function right.