Because the TV show just did something similar? There was an episode just after Crisis. spoilers:end of spoilers
All of the Harrison Wells have been placed in the mindscape of Nash Wells, the last survivor. Including Eobard Thawne, who was wearing the face of Earth-1 Harrison. Eobard managed to take over Nash's body. They had to exorcise him, leaving Eobard incorporeal.
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Didn't he get killed off in Legends of Tomorrow?
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The Crisis does offer an easy out. A few people were resurrected by the Crisis. In fact, a lot of stuff from throughout both Arrow and Flash now happened differently, especially anything involving Harrison Wells, Black Siren, Jesse Quick, and anyone else who isn't from Earth-1, Earth-38, or Black Lightning's world.
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Should had recasted for this new world.