Draiss kept the portal up, as his spell drained the 'food' eventually figuring that most of the shadows would flee to the high magic and underground areas of the death world, where they would be dangerous, but not in sufficient numbers to be a real threat to those with force protection spells. He left the portal on the second level, and set up more lights to drain the magic that would still be stagnating in the area, before heading down, and repeating the process until he got to a level where the shadows actually seemed sentient. The portals he set up for the shadows to use were about the size of his head, and in out of the way places where an organic or construct couldn't accidentally go through them, and were one way portals, so shadows that went through couldn't come back.