A contradiction in terms is a logical inconsistency. There is nothing logically inconsistent about valuing one’s life and yet being willing to sacrifice it for a good cause. Which plenty of people we admire have done through history.
Also, “indifferent” is a technical term here, it doesn’t mean that one doesn’t care. It means that the thing doesn’t make you a better or worse person, which is the goal of Stoic training. Being alive doesn’t make us good or bad.
Examples? Plenty. People risking their lives for strangers or for loved ones, in all sorts of situations.