If it happens and we tried our best but we still all die, what is there to worry about really? There was nothing more we could have conceivably done, and honestly I'm not afraid to die because I'm going to die one day regardless. It's regrettable that future generations (given that this isn't some wild conjecture or something, I haven't begun reading into it yet to see if it is) will no longer to be born, but honestly a day is going to come where humans will no longer exist. Until then, we are just prolonging the inevitable, it's the way things have to be. We should still take steps to prevent it if we can, but squandering our time here worrying our asses off about it is pretty useless and counter-productive in my eyes.