Slade, along with every other residents of Earth-1, was killed in an antimatter wave that was sent by the Anti-Monitor on December 10, 2019. However, due to Oliver's sacrifice, he was resurrected on Earth-Prime.

Who kills Deathstroke?

Batman and Robin

Batman defeats Deathstroke by taking advantage of the two-way connection between him and Robin by using a taser on Robin, the resulting electric shock overwhelming Deathstroke's enhanced senses.

What season does Deathstroke die in Arrow?

Deathstroke's Skills Are the Key to 'Arrow' Season 6

In the final moments of Arrow's shocking Season 5 finale, Oliver watches helplessly as Adrian Chase shoots himself in the head, triggering a bevy of explosions on Lian Yu.