First off there will be a Diablo 3.
Tool is a fool

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And how about Diablo 3: Demise of an Angel
Going to the story line of a corrupted Tyreal such as what had happened to Izual?
Where as the Worldstone had actually never been needed to be destroyed. . .And Tyreal had done it for his own selfish reasons. Where as later on as you develop more of the story line of the game, you find out that the original Diablo (D1) was a clone, and the one from Act 4 in D2 was a reincarnation of the clone, and with the 1.10 patch DC had gotten out of the real Diablo's control, and when you get to the final Act or Stage/Level you find out that the real Diablo was none other than Tyreal. And you must fight him before he is able to transform (you beat him but he transforms anyway) and you now face a Super Diablo?
Or how about Diablo 3: The Leads to Tristram
Or: Diablo 3: The Entrapment of Mephisto
Both prequels to Diablo 1?