Poro only cares about finding Delkira, he doesn't care if Delkira is still King or not.
Honestly, I'm not so sure, especially judging from Poro's reaction when one of Baal's subordinates implied that they can revive Delkira (which implies that he's dead), in which Poro beat the subordinate up until he rephrased his words. Followed by Poro saying that Delkira was his, and should've also been Sullivan's, everything and that no one could replace him. I think that implies that Poro won't accept another king. Now if Delkira ever told Poro that he didn't care for the Demon King's title, then sure Poro wouldn't care either. But as it currently stands, Poro seems to make an effort in preserving Delkira achievements and goals, which also includes the current demon world, and having a new Demon King would also effectively change the demon world.
So it just seems odd to me that Baal is doing this right now, unless either he has Poro completely under his control or subdued, has no need for Poro (and has a backing that's greater than Poro), and/or his plan also has a solution to handling Poro in the event that he moves against Baal.