I still get the impression that was Myrkul's doing via Balthazar.
Though, this leaves the bizarre notion of Balthazar, with the power of Myrkul... Somehow managed to not only pass all of Shar's trials, but also enter Shadowfall and use magic to bind Aylin to Ketheric all without Shar herself noticing or doing literally anything about such a tresspass.
Well Balthazar was with Ketheric when Aylin was first trapped for one and he couldn't have gone back recently, given one of the keys is with Yugir.
It also doesn't really make much sense that Ketheric was immortal before being defeated, by the Harpers and Druids, because he died.
Being given immortality after being reanimated also doesn't work because Balthazar couldn't have entered the Shadowfell, as per above.
