You can stop the mission at any time. If you want to stop it after it completes the flight path and then fly it home manually that is up to you.
Grid flight is supported if you are on at least the Base plan.
You can set the aircraft to fly to a predetermined amount of time or allow the smart battery to do its thing by triggering a return to home. When it leaves the flight path it will drop a blue abandonment point which it will return to after it comes back and you change the battery.