It's now officially confirmed.
Thanks to TVBuff65 for the heads up.
John Barrowman tells crowd at #PlanetComicCon he will NOT be part of DC universe next season. đŸ˜ #Arrow #Flash pic.twitter.com/CmSZd9uWhN
— Pilar Pedraza (@Pilarcita) April 29, 2017
SPOILERS!!!! Says it's because he died in Flash musical episode so will die in Arrow as well.
— Pilar Pedraza (@Pilarcita) April 29, 2017