If an AI hero is displaced back into its own fortress, it will deploy again the following wave (at the bottom of the deployment stack).
Note that per the solo rules, and AI minion can only displace a hero if it has a talent that does so, or if during its movement it must in order to use its full movement and make as much progress as possible. If the minion has an equivalent movement option that doesn't displace the hero the minion must take the alternative option instead.