Luna doing her Oracle stuff was what was holding back the Scourge, right? So her dying is what made the whole eternal night thing happen.
We’re also told that making these pacts with the gods is wrecking her physically, with her telling Ravus she doesn’t know how long she can hold out. The “I know the price of the covenant” implies making one with Leviathan is going to finish her off.
My question is: did Ardyn a) just make the eternal night look like his fault by b) half-assing his Sephiroth impression by murdering somebody who was dying anyway?