Last dupe refused to die until new dupe spawned

I was waiting for my last dupe to die off at the end of a failed game, but he just kept on keeping on in spite of being out of resources. Instead, he died immediately when the next dupe showed up. At the time I thought it was a game mechanic, like you get to keep one dupe at all times so that you always have a chance to "save" a colony after a mistake. I don't remember what he was dying from but it was probably lack of oxygen.