How it’s all going to end
The key to the series was Season Five’s 16th episode, The Incident. This is how the show is going to end. Just like MIB can be numerous people (MIB, Locke, etc.) so can Jacob. So at the end of the series, I am unsure of how they will exactly get there, it is going to be new Jacob portrayed as Jack and new MIB portrayed as Locke. The two will be sitting on the beach just like in the episode, The Incident, and a new boat, plane, train or taxi filled with new people will be on their way to the island to start the process all over again.