Ideally, you wouldn't let races die out as it's directly contrary to your goal. However, it all comes down to Synthesis points, which are gained via disasters (either in events like these or in the campaign map, where you can devastate non-sentient planets for a small trickle of synthesis). The best outcome in any situation will demand Synthesis; the worst will give it to you. So do you just let a people meander towards a probably interstellar population? Or do you let die in a grand conflagration to gain Synthesis points to boost your favorites?
