That was a shock and a half - I really liked Kutner
It really seems to be a trend, killing off main characters lately, everyone seems to be doing it, sigh.
Apparently the actor has been offered a job at the White House. While the writer's strike was on he apparently was working on Obamas campaign, too. From what I understand it was the actor's choice to leave the show, the writers didn't off him for shock, but certainly no one can ask him if he is coming back at a later date, its a pretty final ending for the character.
Someone did mention on another site, why not just have him leave for a better position, etc., but I don't think that would have worked - too easy for House to torture him, plus they did that with Taub already. This might be the only way out, so to speak. However, now they have material for the rest of the season, it will be interesting to see how the mystery is solved. I am guessing that the thing House realizes is missing is - the suicide note. There always seems to be one, somewhere...? I guess we will have to see how it all plays out.
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People think there are four elements to the world; fire, wind, water and earth. They are wrong. There is a 5th element - surprise. - paraphrasing of Terry Pratchett "The Truth"