It would be a great idea for a game like, imagine if you just killed the main boss or complete your task but you realise you've done a grave mistake and a wall just spwaned dividing the world and then you come to know that there wall was always there but you couldn't see it because of some things or other stuff slowly the wall starts to weaken and break and the catastrophe on the other part of the wall starts spreading. It reminds me of terraria.