It would re-impose the Partition Plan and deploy an International force to implement it. Israel agreed to borders as defined by the Partition Plan in 1948 and has not legally changed them since therefore it must be guaged it is happy with those borders. Therefore all those settlers beyond those borders can be automatically made Palestinian Citizens when UN reimposes the Partition. They would then be subject to Palestinian Law. Sometimes the simplest option is the best one.
Boko Haram militants kill 11 Chadian soldiers (Reuters)
from the article: UN to aid Palestinian victims of settler violence in West Bank