Вот так попробуй

Код:
public override void OnActorCreated(int missionNumber, string shortName, AiActor actor)
        {
            base.OnActorCreated(missionNumber, shortName, actor);
            if (actor is AiGroundGroup)
            {
                if ((actor as AiGroundGroup).Type() == AiGroundGroupType.Ship)
                {
                    Timeout(3300, () =>
                        {
                            if (actor != null)
                            {
                                (actor as AiGroundActor).Destroy();  // уничтожаем
                            }
                        }
                    );

                }
            }
        }