Humanity is dead, I fear. What can we do but pray.
My first reaction on hearing this news was to yell out "NO!" over and over again, and then to conclude just as you did. Prayer is not the last resort, it is our best offensive weapon against the kingdom of darkness.
[F]or the weapons of our warfare are not of the flesh, but divinely powerful for the destruction of fortresses.
2 Corinthians 10:4
God must be fed up by now. Get ready for a bumpy ride. I think He's getting ready to do something big...