Two weeks ago I tried to speculate on a complicated scenario for the IC "kidnappings", but it was a very simple, one-shot affair.I can't see MB making this twist more complicated than he has to, either. I think it will be a one-shot affair.
My guess right now:
The Ghost Tribe will consist of Lillian, Burton, Michelle and whoever gets voted off this week. Maybe Nicole and Ryan S. are in it too, maybe not.
They get to compete against Drake and Morgan in the first challenge in Episode 7. If, and only if, the Ghost Tribe wins, one player from that tribe can come back in the game, supplanting one player from the tribe that comes in third.
If the Ghost Tribe doesn't win, they're gone, forever, and the game resumes as normal.
Hence Burton and Michelle "come back" to compete in the challenge, but only one person (Lillian) actually re-enters the game after the challenge -- assuming that the Ghost Tribe does win, as Griffe reported above.
Now, how MB would determine which player from the winning Ghost Tribe returns and which player from the losing tribe leaves, I don't know. But once all this is accomplished, everyone left merges into one tribe, and the game continues.
Maybe.