But doesn't that mean that the Earth has practically no nuclear weapons left?
Oh, no, that's terrible! Whatever shall we... Hold on... wait a minute... hmmm.
But seriously... I would imagine that a country's nuclear arsenal would include a number of inactive and/or reserve missiles in addition to those at launch-ready status. So even if we were meant to believe that the missiles somehow managed to reach escape velocity, or explode harmlessly above the atmosphere, there would still be a partial complement of unspent missiles remaining. So you can rest easy that the capacity of the world's nations to inflict pointless and devastating mass destruction on one another would not be entirely lost.