1. Could it be possible Adria becomes Diablo in the betrayal? I don't remember a confirmation that Adria is dead, and she could be assisting the Hells to become Diablo or at least be serving him by betraying Azmodan. She did have relations with a former Diablo after all.
2. My own speculation: The original Soulstones are made out of pieces of the Crystal Arch, not the Worldstone.
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1. Could it be possible Adria becomes Diablo in the betrayal? I don't remember a confirmation that Adria is dead, and she could be assisting the Hells to become Diablo or at least be serving him by betraying Azmodan. She did have relations with a former Diablo after all.
2. My own speculation: The original Soulstones are made out of pieces of the Crystal Arch, not the Worldstone.