The Keys aren’t simply for his freedom. The Key he grabbed from the Archon is specifically for Korthia.
The Jailer seeks the Broker’s Realm Korthia to locate the place that the Arbiter’s Key unlocks! The Key to the Maw is inside the Heart of the Forest. Get that and the Jailer can escape easily!
Blizzard has stated that Ardenweald is the next target of the Jailer aside from Korthia so his escape is indeed happening now that he has Korthia unlocked.
Once he has his freedom and the secrets of Korthia he is ditching the Maw for the other 2 Zones he seeks to gain access to!