The relic isn't safe in the Shadowfell, neither Balthazar nor Thorm are Sharran anymore, they're probably afraid Shar will decide what to do with the Nightsong that doesn't aid her rivals.
Do we know that Ketheric was resurrected? I thought that he has just been stewing in moonrise since the curse. On that point...the curse is Sharran in origin, was it put on Thorm after he renounced her? There used to be a book in the EA where Thorm was described as getting too big for his breeches, which was implied to lead to his downfall. I'm pretty sure Balthazar is referenced from before the cursed times, but it does make more sense if he's only brought on as part of the Crown gambit, explaining why Thorm now follows Myrkul.
Well, he had to be ressurected.
Balthazar is the one who brings along the Soul Cage with him in 1482, therefore Ketheric must have died those many years ago as he couldn't have been invincible just because Aylin was trapped in the Shadowfell. And no, there is no trace of the Shadow Curse on Ketheric, and is never shown in the game or other books and notes to have ever been affected by it or gotten close to it without the proper protection. Balthazar does appear in the original downfall, but he couldn't have been following Myrkul then given Myrkul was dead at the time? We would have had to be Sharran.
As for any possible Shar intervention, She couldn't care less if Aylin is used as a source of invulnerability. If anything, it is a giant win for Her to have Aylin imprisoned and wait for a faithful Sharran to find the Spear of Night and kill Aylin for good - which is something that happens with Shadowheart.
On another note: I will update the OP with all the new info we all put together just so that future readers can be on the same page as well.
