"The chances of a complete recovery after the modern surgery are estimated at 85 to 90 percent." - http://www.baseball-reference.com/bullpen/Tommy_John_surgery
"124 Major League Baseball pitchers and counting had Tommy John surgery." (1994-2010) - http://tommyjohninformation.weebly.com/statistics-and-percentages.html
A few pitchers have had three TJS and still been okay after (Jason Isringhausen, Jose Rijo).