I have a feeling it won't happen -- lack of faster-than-light travel, and all. (Not even going to address the question of whether or not there is life on other planets, I just think it's moot for them, just like it is for us.)
I think we're just procrastinators. I mean, at a racial level. When we realize we're going to run out of oil, or accidentally killed one too many key species in the food chain, or accidentally opened the hole in the ozone layer too wide, it is my belief that then we'll finally do something about it. It'll be almost too little too late, but there will be enough survivors to continue.