Tristan is one of a number of International Solidarity members who have been either killed or critically injured during protests of occupation. Rachel Corrie (killed 16/3/2003; Wiki), Brian Avery (shot in the face and seriously disfugured 5/4/2003; Wiki ;Democracy Now interview 2005) and Tom Hurndall (killed 13/1/2004; Wiki).
The last recorded piece of information I can find of Tristan's condition is 31 March. He was still in intensive care.
Details of Tristan's condition can be found:
Tristan was friends with Brad Will a peace activist who was killed while filming the Oaxaca City teacher's strike (and subsequent riots) on 27 October 2006. The riots are alleged to be in response to political corruption.