However, these two episodes are at best a taster of what’s to come. In “The Sandman,” Derek watches his wife get shot. In “A Beautiful Disaster,” he gets caught up in a blood-curdling game of Russian roulette with his sworn nemesis, Chazz Montolo (Lance Henriksen). The agent loses. For his last wish, he begs him to call the BAU team. Chazz obliges. While talking to the team, Derek grabs his arm, pushes him to the floor, and wrestles him down.
The BAU team arrives on the scene in no time, and Derek is let free. However, the spine-chilling scenes mark his last few moments on-screen. The turbulent events led the agent to quit, choosing to spend some time with his family instead.
Source : https://www.distractify.com/p/what-happened-to-agent-morgan-criminal-minds