Sunset is the euphemism NCsoft used for the closure of City of Heroes and the firing of nearly all Paragon Studios employees.
The sunsetting process was announced on August 31, 2012, also known to the community as Black Friday, coinciding with the elimination of all Paragon Studios job positions but two community managers (Zwillinger, who left a few weeks later, and Hit Streak, who remained until the final closure). The servers were maintained by NCsoft employees in Austin, Texas, so they continued to oversee them during the sunset. However, regular weekly maintenance was stopped and they only performed emergency maintenance during the three-month sunset period. No patches or even bug fixes were implemented following the announcement.
The actual sunset, when the servers were brought down one by one, happened on November 30. The Beta Server was the last to shut off just after midnight, December 1, 2012. City of Heroes was officially closed.