i was searching for possibility to deactivate servo, to prevent damage (overheat) it in my case, and finally I have found a solution. You have to set "!" in front of pin name and then again any M280. "!" changes polarity of output and next M280 command results in sending unreliable data to servo so it deactivates.
Like in example bellow.
Of course then before any M280 command you should put M950.
M950 S1 C"pinname"
M280 P1 S180
M950 S1 C"!pinname"
M280 P1 S180