While the Season 12 finale involved a couple of exits, it did feature a major return.
However, fans remained hopeful that Hetty would return, and so she did in the finale.
Linda Hunt, who has portrayed Operational Manager Hetty Lange since the first season, was absent through much of Season 12, due to COVID concerns.
While there really wasn’t any explanation for Hetty’s in-show absence, it’s possible that Season 13 could explain why she’s been gone, or the writers may just keep it a mystery, seeing that most fans likely know the real-life reason for Hunt’s absence.