Canons 290-293 (http://www.Vatican.Va/archive/ENG1104/__PZ.HTM) states only a "most grave" cause can release a cleric from the clerical state. No proof of a criminal act has been revealed against Archbishop Nienstedt, as per the Ramsey Country attorney's office. He has not been proven guilty of any crime or grave act and is therefore innocent until proven guilty.
If he knew about the abuse and permitted and aided the offenders being reassigned instead of punished, he should resign. He should still be permitted to as God and those who were harmed for forgiveness, but he shouldn't have any of the perks of a higher office. If he's still a member of the clergy, he should live simply and serve away from others.
Archbishop Nienstedt should no longer be a member of the clergy. The archbishop acted contrary to beliefs of the followers and other clergy in that an archbishop should be a very moral and good person. Bishops and priests are expected to be a figure people can look up to and trust. With the sex scandal Archbishop Nienstedt should be removed from the clergy.
The clergy are some of the formal leaders within certain religions. These people should be upstanding pillars of both religious and more widespread society. Their obligation is to uphold the law in every such way and being that Archbishop Nienstedt is involved in a scandal he should not be allowed to still be a member of the clergy. It sends a message of ignorance and acceptance when really they should be the members of society which first question this type of crime and are the last to engage in it in any such situation.
Any person that either perpetuates or hides child sex abuse should be kicked out of any leadership or employment with the church. The church needs to think about its own public relations and also about the many helpless victims that suffered because of silence and because of covering things up. The church needs to take a hard stand against abuse by making an example out of abusers.