For who dropped below the map and don't want to restart the game losing the save file follow these step:
- close the game
- download and install this save editor https://github.com/trumank/uesave-rs/releases
- go to C:\Users\USERNAME\AppData\Local\PokemonEmerald\Saved\SaveGames
- open a terminal here and type "uesave edit Slot1.sav"
- go to line 347 and change the x to 139584.0, the y to 35.1959228515625 and the z to 68.11904828200309
- save the file and restart the game.
You'll spawn in front of the first pokemon center tent and can continue the adventure