Contrarian take, a scarily plausible nightmare scenario:

The year is 2058. Humanity is extinct due to not solving the AI alignment problem before deploying superintelligent systems. The Earth and its life is being disassembled into raw materials to build computronium. Von Neumann probes are being sent out to disassemble the Solar System. For what purpose, only God knows, but probably something we would consider pointless, like maximizing paperclips. It will rapidly expand to the limits of our Hubble volume as fast as the universe allows. And nobody will be around to watch.