Step 1: Be in Act 3, learn from the Steel Watcher that Karlach's heart is an early version of theirs. Step 2: Rescue Zanner's daughter, tell him. Step 3: Clear the Steel Watch Foundry Step 4: Tell Zanner about your issue Step 5: Compassionate because you saved his daughter, he builds a final heart with Dammon for Karlach.
3/5 of these are already ingame and provide a much more satisfying ending than returning to Zariel's service, which is something Karlach clearly doesn't want to do. She wants to live, on the material plane, and the pieces are right there.
This is actually EXACTLY what I was thinking as well, outside of just having Gale with Mystra's help/the crown magic her up a new heart. This even neatly ties it all together in a gameplay sense by making her happy ending very annoying to get, since you'll need to go to the Iron Throne and rescue everyone (which is also what makes Wyll's happy ending with his father if you break the pact very annoying to get as well). You don't just hand the happy ending to the player on a silver platter, but you do make it actually possible and it MAKES SENSE.
Exactly. While there are 10s of solutions present, the fact that there's such a clean one that fits into the arc already is the stinger.
