"Leaving it in the box" is merely leaving the decision between death and release to the next person to take the post. There are only two terminal conditions to the situation. If only one of these options is acceptable to me, I should take it; postponing the decision merely takes me out of the decision-making process.

Don't mistake me: I'd risk all of civilization over a matter of principle, and I wouldn't wish while I did it that I could have a different decision-making process. And I'd consider the matter "won" regardless of the outcome - I don't find "ends" to be a coherent ethical concept (counterfactual logic to some extent remedies the major faults in ends-based reasoning, but counterfactual logic isn't exactly coherent itself), and so consider only the means.