var bodyExtractor = [Game.CARRY, Game.MOVE, Game.WORK, Game.WORK, Game.WORK];

Game.spawns.Spawn1.createCreep(bodyExtractor, null, {role: "harvester", set: "extractor"});

I have had this working for weeks, and on open world all of my stuff is braindead.

This code has been going around since the dawn of Screeps I think originating on the website StackOverflow.

for(var i in Memory.creeps) {
    if(!Game.creeps[i]) {
        delete Memory.creeps[i];
    }
}

It simply removes creeps from memory that are no longer living. I usually place this somewhere where it can run every tick.