From http://neo.jpl.nasa.gov/news/news149.html:
"The asteroid's motion subsequent to the 2029 Earth close approach is very sensitive to the circumstances of the close approach itself and a number of future Earth close approaches will be monitored as additional observations are received"
So after 2029, all bets are off, well need to recalculate the trajectory.
:') I was just updating from the NEO program page (NASA/JPL). The odds in 2036 are shown as 1:13,000, but from what I read on the page you linked, the claim is that there won't be any 21st c encounters in which the Earth will be at risk. Guess I'd better read some more...
http://neo.jpl.nasa.gov/risk/2004mn4.html