It is not confirmed that he died. The only proof that we have that he died is that Desmond said so, and he was frantic at that time. Also when the tailies, Michael, Jin and Sawyer are walking to the beach camp, they pass a place that looked like the place where Kelvin was presumably killed -- but there was no body. If this was the same place, the Others might have taken the body.
Comments?
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http://www.lostpedia.com/wiki/Kelvin
Look under the trivia section.