Individual post-mortem rebirth aside, sentient beings in general continue to be born. The process of birth, life and death continues, irrespective of whether it happens to any one individual once or multiple times. Judging by the news and simply observing one's personal experience, it is clear we are heavily affected by greed, hatred and delusion, for which Dhamma is an antidote. In the future, we may succeed in colonizing other parts of the universe, bringing with us our afflictions.
Again, putting aside this one question, is the course of sentient life aided by following the Buddha's teachings, or no? If everyone on the planet learned to practice anapanasati or satipatthana, or simply followed the five precepts, or contemplated impermanence and the ephemeral quality of "Self", would this be a net benefit, or would it make no difference?