The thing that is odd in all this scenario is that, if they would have told the present cast that next season is the last and will be shorter, why would not they got the full cast to do the type of Going Home thing?
That is why i think there is more to it, that we can think and none of the theories will be correct and who knows this may be the 1st time that the show actually surprises us.
Of course they may end not getting a new season at all and be cancelled, i mean the same happened with Castle, news are sent outside and then fans reacted and they cancelled it.
What if there is a Going Home, but different, that this time they loose their memories, so really a dark curse and that way would explain why certain characters wont appear, because they dont remember each other.
"I offended you with my opinion? Ha, you should hear the ones I keep to myself".