Okay, apologies - you can *actually* tell Mizora to go F herself, break the pact *and* save Duke Ravengard.
Easiest method I've done is
just throw an Invisibility potion on him when you open the door, but before the cutscene. The kamikaze summons won't even move from that spot and you can just run the Duke straight to the ladder.
I want to try this! May I ask what did you do for Karlach's ending? Her's is related to Wyll's and I've heard that
she just dies if you don't make a pact with Mizora
Is that true?