Al-Sadr was just a minor fringe cleric who has only come to the forefront because the occupying forces shut down his newspaper for it's anti-american views and then arrested a close aid. These actions only increased his support base amongst the young shia's with his ultra Iraqi nationalist/anti-american/anti-saddam views striking a cord amongst them.
I personally believe the senior cleric's will alow him to continue because the eventual heavy handed dealing of this problem will only strengthen their cause, and perhaps they will bring him in once they feel his usefulness has waned.
Tronsky