This has come up before:

http://www.reddit.com/r/AskHistorians/comments/1ayqun/what_happened_to_the_tank_man/

• (2 answers - top comment TL;DR: nobody knows, there are claims but no evidence)

As for the "he was never heard from again" that is a pretty vague claim, and in a way it's true, because nobody knows for sure what happened to him after then. But the way it's worded, it might be taken to imply he was captured and/or killed - however, not hearing from someone again is no proof of that, and would still be consistent with him escaping to exile or just fading back into obscurity.

This comment makes some good speculation (which is about as good as you're going to get in terms of answers) and points out that the photographs of the event were taken by western journalists, and Chinese authorities would not necessarily have even known about his notoriety until later when it may have been too late to then find him. But again this is not evidence of anything.