One way or another, they have to try to settle the violent dispute. To many innocent lives are being lost. The good news is I do not think they can make the situation any worse. In the end, I think the United Nations will slowly gain ground, and finally put an end to the dispute.
The United Nations has to work out a peace treaty between Syria and Syrian rebels because all other interested parties won't be objective. Russia and China have foreign investments in Syria. The United States wants Bashar al-Assad out of power altogether. The rest of the Middle East doesn't want to get involved. The UN is probably the only organization that has a chance to broker peace in the war-torn country.
I do not believe the United Nations will be helpful in negotiating peace talks between the Syrian government and the Syrian opposition. The problem with this suggestion is the fact that it has already been tried and Assad can't seem to uphold his end of the negotiating. The UN is somewhat helpless when the leader can't fulfill his duties.
At this point in the conflict, no one (including the UN) will be able to negotiate peace via diplomacy. The Syrian government will win this conflict by military force, or they will die in the attempt. The appetite for reconciliation is not much stronger on the side of the opposition. The only hope for peace is that one side eventually surrenders, or that a major world power (probably the Russians) brings a diplomatic club to bear on the Syrian government (probably the withdrawal of support and weapons).
I do not think that the United Nations will be of any help in regards to the peace talks involving the Syrian government and the Syrian opposition. I think the situation going on in Syria is something that needs to be settled with the Syrian government and the people themselves.