AC servo motors are for practical purposes identical to alternators so yes they will generate a voltage as they decelerate which will be comparable to the voltage that would be needed to drive it at that speed. The theory is more complicated than that of course there will always be a voltage drop due to internal winding resistance. If you were to short out the windings whilst the motor is running which is not a good idea then the motor would stop very quickly. In practice load resistors are used to give a controlled deceleration. The actual voltage and current that will be developed will be dependent on the actual motor,. I am not sure why you use the word inverter which are not generally used to drive AC servo's but either way you should never disconnect a servo motor from the servo drive or inverter while it is still running or coasting down because high voltages spikes can be developed which can cause damage. If you short out the terminals/wires and just try and turn the shaft by hand you will notice that the shaft will be much harder to turn even at slow RPM's at higher speeds it can cause mechanical damage.