If you had an advanced civilization living there for thousands of years, without continuing the labors of terraforming, doing absolutely nothing to prevent that

If you had an advanced civilization living there for thousands of years, without continuing the labors of terraforming, doing absolutely nothing to prevent that from happening (even when they know what will happen, while measuring the atmospheric levels slowly dropping)... maybe they'd deserve to die. I mean, that could only mean that they actually wanted to die!