http://en.wikipedia.org/wiki/Secretary-General_of_the_United_NationsSecretaries-General serve for five-year terms that can be renewed indefinitely, although none so far has held office for more than two terms[2]. The United Nations Charter provides for the Secretary-General to be appointed by the General Assembly upon the recommendation of the Security Council. As a result, the selection is subject to the veto of any of the five permanent members of the Security Council.
The UN Charter's terse language has since been supplemented by other procedural rules and also accepted practices. In practice, the Secretary-General cannot be a national of any of the Permanent Members of the Security Council.If Obama loses, UN is out, as it would be for any national of any of the permanent members of the Security Council.
I he loses, I believe he would head up and participate in think tanks, make the rounds on the lecture circuit, including being a guest lecturer at some of the leading universities in the U.S. and around the world, write some best selling books, appear as a guest speaker for $1,000,000.00 or more per speech, but his main focus would be as an advocate for the disadvantaged.