The universe won't blink an eye, and things will go on. Mankind, even one whole planet, isn't really that important on a universal scale.
I would add that we are not even that important for the earth -- on the contrary. The earth would be much better off if we didn't exist. Dare I say that perhaps we might be working towards exactly that.
We have been terrible stewards of this planet. The industrial revolution, for all the great things that it brought us to make our lives so much better, it also put us on the fast lane towards the precipice.
How do you unwind decades of making financial gain the center of practically every decision that is made? I don't think you can.