DSK did not travel on official IMF business to NY. He was on personal business, to visit his daughter who is a grad stiludent at Columbia.
The IMF has already thrown him under the bus. They have stated he was not on official business and cannot claim immunity under some UN agreement. He is not a Diplomat, does not represent France, and has no immunity.
If he did, do you think he’d be sitting in a cell at Riker’s?
Maybe you should read the articles. In New York state, the law is, it’s up to the courts to decide what official business is. The bottom line is that until the court decides he doesn’t have diplomatic immunity, it’s an open question. His lawyer may be waiting to bring it to the court. The U.S. government usually sides with this type of person over U.S. citizens. If the State Department can have their way, he will be allowed to leave the country.