The whole point is that The One Being is trying to come back into physical existence, but in doing so, merges the realms into one. My theory is that Shao Khan, Onaga, Dark Raiden, Shinnok are being manipulated by The One Being to merge the realms. ( I think of The One Being as something like Sauron from Lord of the Rings ) Fighting is causing the realms to split instead of merge, which is why The Elder Gods impose balance within the realms through the Mortal Kombat tournament. We have already seen Daegon in MK9 background, so it's probably safe to assume that we will see Taven again.