The Legends of Tomorrow lead will guest-star in the Season 6 finale, although the circumstances of her visit have not yet been revealed.
One wildcard at play regarding Quentin Lance’s exit is the arrival of Sara Lance.
Sara could be on the scene for her father’s funeral, or she could arrive and extend an invitation to her father that’s less playing dad to a doppelganger and more linking up with her and the Waverider crew for some adventures.
Paul Blackthorne departing Arrow for Legends of Tomorrow would be an awfully strange move, even for a show as weird as Legends, but with EW short on details of how this exit will go down, anything is on the table.