Them standing in place is just them waiting for a new objective. Maybe there could be a small system put in place where units in this situation were put on ambient movement/patrol until they are given new orders. I definitely agree that it would help immersion greatly. Probably a post 1.0 improvement since they are planning to greatly increase the depth in which AI are tasked/controlled. You can submit any suggestions and view the roadmap at the Dev Heaven page: http://dev.withsix.com/projects/alive/activity
AI reacting to User made tasks is a future goal they wish to make happen.