What will the rubber band do at the end of the dread? And how long should you keep it there with neglect method?

The rubber band at the tip is used to help keep the dreads together when they are new and it helps the tip lock up once the dreads are tight. If it is just a regular rubber band then you should just leave it there until it falls off, but if it is one of those super Scunci elastics then it will never fall off, you should take it off after three months.