) 2029. 
1 in 6,670 chance
Analysis based on 2 radar delay, 3 Doppler, and
700 optical observations spanning 376.73 days
(2004-Mar-15.10789 to 2005-Mar-26.84181)
From your article (which you probly did not read the end of)
They were. On Dec. 27, Spacewatch astronomers Jeffrey Larsen and Anne Descour found 2004 MN4 in a series of images taken March 15, more than three months before Tholen's sighting. They passed the word to JPL, which issued a news bulletin: "An Earth impact on 13 April 2029 can now be ruled out."
You need to understand that the more observatiosn made of a object, the more certain you can be of it's flight path. The probability will steadily go down, and the will measure how far from the earths center it will be. Granted.... it will be close, but there is very little chance of it becoming a "Doomsday" asteroid
