User blog comment:Undead Chosen One/Diablo/@comment-26096179-20200119011638/@comment-26096179-20200124054748

Most likely not, he was released from his imprisonment within the Black Soulstone, containing the essences of the other Great Evils. Only time will tell.

In the sense that the two fought one another in the High Heavens, with Imperius holding a grudge against Diablo, yes. With time, Imperius could develop his grudge for humanity even further, letting it corrupt his senses/thoughts & plot together with Diablo himself against all of humanity. Once again, only time will tell.

Best wishes