Usually a game has a "main loop" for everything that needs to run during the game. Loading the map itself is usually outside this loop; that's why you see loading screens before beginning a level in real games. The main loop then handles moving the view around the loaded map, moving the characters and enemies around, and handling all the damage and whatever.
HOWEVER, if you go into a new area that requires a new map load, you usually briefly exit this loop in order to load the new area, then reset all the enemies before jumping back into the main loop. This can be done with things like GOSUB or functions.
