According to what malicat mentioned above, the showrunners claim to have plans for Rip next season, so I believe he'll be back. He just won't be part of the team, at least not immediately. I feel like Rip needs time after everything he's been through, but he must know that he is just still much part of the team and family aboard the Waverider no matter what. He and Sara becoming co-captains is not an impossibility, it actually makes perfect sense considering that they were kinda already doing this in a way.