I think they could do an alternate universe crossover. Have the after credits screen with the 2016 cast involved in a climatic battle similar to the one just concluded in Frozen Empire but they are losing. A portal appears and The Originals step in. “Didn’t we just leave this party?” There is a bit of witty dialogue between the OG’s and the 16’s including a request that they come to our universe to help out with a larger issue. The 16 cast agrees. They all group up in a hero shot of the ensemble and “on the count of three, go on two”… re-join in the battle.