The events of Part 4 of the Arrowverse crossover was decided a long time ago. "I know that Marc (Guggenheim) had discussed it with Greg (Berlanti) and that is how we would end the series," says showrunner Beth Schwartz. "So that's how it came about. And obviously this is our last season, so it all kind of worked out." ALSO: Arrowverse boss Marc Guggenheim answers burning questions about the final two parts.