[FG28_Kodiak]

1) they stay destroyed

2) Radars are no GroundActors they are static objects so you must use the new OnStationaryKilled (works since the latest beta patch)

public override void OnStationaryKilled(GroundStationary _stationary, AiDamageInitiator initiator, int eventArgInt)
{
    base.OnStationaryKilled(_stationary, initiator, eventArgInt);

    _stationary.Destroy();
}