While on the subject: A brush-type servo doesn't need returned energy protection because it cannot generate any in normal operation. The motor 'back EMF' is proportional to speed, speed is limited by the supply voltage, therefore all voltages are equal to or less than supply voltage. No 'returned energy'.
1) There is energy stored in the motor's inductance. This is a minuscule amount compared to stored mechanical energy and can be safely neglected.
2) During an e-stop you do want to stop the motor quickly instead of leisurely coasting to a stop. The original circuit doesn't address this while all three of the circuits I posted do. The 'dump' circuits dynamically brake the motors to a stop when AC is removed to the power supply. The motor becomes a generator working into a large load (dump resistor) which quickly extracts stored mechanical energy from the motor and mechanism.