The survivors of the cult splintered and became a bit of a running gag, but yes, the players were a bit pissed that the big bad of that part of the campaign was dead off screen.

I don't really do a singular big bad... Just groups and factions and madmen wanting power.

The players run into some of it. And hear tails of other adventurers solving some of it off screen. Which is what they thought happened at first until the wizard made a great roll and spotted an error in the ritual circle.