Escaped or set free?
Yet to be revealed. The current fluff as it stands in The Wrath of Magnus
is that the Changeling had infiltrated the DA, fooling them into the attack on the SWs. When revealed, he is persued through the Rock by the DA hierarchy, along with Ragnar Blackmane, a GK captain, and an Inquisitor, IIRC. He seems to be heading deep into the most secretive parts of the Rock, able to access doors and vaults only Azreal should have been able to. He gets banished when a Watcher appears...
"...the Changling found his way barred: not by the embattled heroes, but by a diminutive figure that was hidden entirely by white robes and carried a graven crozius in both arms. The Daemon recoiled in horror, for the creature before it was anathema to its kind. The creature focussed its baleful glare, and the Changeling turned and fled."
This would not lead you to think he'd managed to set Luther free, but I think we'll see a campaign similar to Warzone: Fenris to tell us the whole story, and reveal the Lion to his brother. Also, 130 years have passed in the timeline since that, so anything is possible.
Imagine how pissed the Lion is going to be when he wakes up. Thought he should have been made Warmaster, doesn't get it. Was never a huge fan of Girlyman, and after sleeping for 10,000 years, he's probably expecting to finally be the main man. But oh no, there's Girlyman, fresh as a daisy, running the Imperium again. Frustrating to say the least.