“Reunion” is episode three of season four of Stargate: Atlantis.
Colonel Samantha Carter does not merely make an appearance in this episode, she is the new commander of Atlantis, following Dr. Weir’s disappearance and presumed loss in “Lifeline”. The Wraith and the human-form Replicators are attacking each other, showing that the mission to get the latter to follow their original programming was successful.
Meanwhile, Ronan meets some Satedan survivors on another world, who invite him to join them, an invitation that leaves him torn.
There is also a brief appearance by Teal’c.
It’s possible that Dr. Weir will return at some point in the future, given that she is still being mentioned, although it’s likely she won’t be back in the same role.