It doesn't make what has transpired any less hopeless or depressing, but the last shot of the film is an act of human kindness.
Even as horrifying as nuclear war is, there are survivors. A lot of people died, and many more will succumb to disease and/or hunger, but some will survive to start over.
The fact that in Real Life, this film contributed to a push on both sides of the Cold War towards detente, ending a period where nuclear war fever was at its highest since the Cuban Missile Crisis. In short — we are here on TV Tropes and not radioactive ash in part because of this film. On behalf of everyone here, thank you, Mr. Meyer.
No less a person than Ronald Reagan made a point to thank Meyer, sending him a letter after finally making a peace treaty with Gorbachev, which read, "Don't think your movie didn't have anything to do with this...because it did."