The writers for “Supernatural” have always been pretty good at dealing with consequences, so this episode was not unexpected. There had to be some fallout from the arrival of the apocalypse and Sam’s role in it. What could have been a rather predictable set of circumstances, however, takes a delicious turn.
A number of people predicted that Sam was supposed to be the vessel for Lucifer, and had the Brothers Winchester not been removed from the spot where Lucifer rose from the pit, he might well have been. Instead, Lucifer is tracking Sam down so he can manipulate Sam into consenting to possession. That is unlikely to end well.
After all, if Dean is fated to be Michael’s vessel, and Sam is fated to be Lucifer’s vessel, then the story is rushing towards the kind of brother vs. brother conflict that has been in the cards since the second season. I doubt it will play out quite that way, since the writers have successfully taken the story in other directions before, but it does seem to suggest that Sam and Dean will be separated for a while longer.