Your position in keyword ranking is determined by quantity of installs that your app recieves in comparision with other apps that are ranked for this keyword. If you get your app to some rank by some keyword, and stop promoting it might stay there, if organic installs for your app are bigger than organic installs for your competitor apps, this is influenced by your app icon, screenshots, description, and if it is relevant for the keyword you got ranked. So we don't guarantee that your ranking for keyword will stay, as we can't influence your app relevance, icon, screenshot and desription.