You can probably leave if you're a dungeon explorer but I don't recall there being mention of a door leading out of the dungeon. That being the case you'd either have to clear the dungeon or survive in it long enough for it to turn into a field dungeon. If there were people scouting the dungeons then why has Shin been given no such information on the dungeons? Elemental resistance only accounts for the most basic attacks she could make. Like throwing ice shards or freezing them. Making them shatter or melting them would probably still work. Them being monsters would probably make it harder but not so hard that it's impossible to control them.