I had an old save right before Mizora offers the new deal, so I just reloaded to test. I still didn't get the option to tell him to make a choice. Karlach's reaction is still bugged, and she thinks Wyll gave up his soul to Zariel. I do like the part of her line where she says "There's such a thing as being too good. Someone ought to tell Wyll Ravenguard." I love Wyll and Karlach's friendship.