When we talk of aliens, we need to stipulate a) that it's 'intelligent life' we're talking about and b) that it's contemporaneous intelligent life we're talking about.

If mankind fails to reign-in its greed (more specifically, the greed of entrepreneurial monsters), the world will almost certainly continue to suffer. What the breaking point is, no-one knows and when it will happen, no-one can say, but the distance we've come since the industrial revolution (and the damage we've done to the planet in that period) hardly leaves me optimistic that we'll survive much more than a century.

Will we 'reach for the stars'? (Like in the films, say.) Maybe a few filthy rich entrepreneurs will time everything right to be able to leave the planet when we're knee-deep in a swamp by having craft ready, and take the opportunity to do so, but maybe they won't be prepared in time through lacking necessary technologies.

So, alien life, intelligent alien life, will they be around / still be around in this window of opportunity? If they've not yet discovered how to travel distances measured in lightyears, then maybe all this is a moot point as we'll never get to meet due to physics. My very smartest money is on the bet that we'll never discover extraterrestrial life wiser than an amoeba. But it captivates people and makes for great sci-fi so we can all still live intrigued by the prospect of others (preferably non-hostile others) being out there and en route to an as-of-yet unplanned rendez-vous with us some time in the not-so distant future.

Were we to detect intelligent life, communicate with them and even plan such a meet-up, I would expect it would require a generational thing. It would be the very distant descendants of the original pioneers who would get to enjoy the experience, I'd imagine. We'd need big craft, improved recycling works, willing participants and nuclear power powering it all. Not impossible, just hard to pull off, I'd say.