Before Year Five
After establishing the Regime, instead of rooting out the criminal Deathstroke like how it is done with other criminals, Superman decided to let Slade go. Slade took this opportunity to retire, and is never mentioned since.
In his retire, it is implied that he was frequently contacted by Lex Luthor, in an effort to have Slade join the Insurgency, but Slade refused all of them.
In an effort to take down the Regime, Batman visited the retired Deathstroke, who is enjoying himself at Bali, Indonesia, hiring him to steal the Mother's Box. Intrigued by a "Suicide Mission", Slade accepts the job.
Slade infiltrated the Armory, taking out guards before retrieving the package, then took out more guards, before being hit by Metamorpho. After finally became aware of Metamorpho's presence, Slade engaged him in combat. At first it appeared that Slade was no match to Metamorpho, but Slade managed to knock out Metamorpho using a surprise bullet misfired earlier.
As a fail-safe, Deathstroke scanned the Mother Box's model, and sent it to Batman. He finished just as more guards arrived as he exfiltrate. Before he finally succeeded the run, he is pinned down by Cyborg, and is captured by him and Raven, just as Deathstroke expected from the Regime.