You have to call here in a SnG. Either you're tripling up, which allows you to make the money and get at least second if you are near equal to the other players, or you're out and get started in another SnG.
I've been in this situation twice (once vs one opponent and once vs two opponents), both times I had the best hand going in and both times KK held up and I went on to win one and get second in the other. One time I was heads up against JJ, and the other time I was up against AK and TT.