Finally I managed to wiggle my way out of the demon realm! Yes, it's true. Even although it's monumentally hard to do so, just keep trying and eventually you'll get it (previous posts in other threads stated it would be impossible to ever get out of the demon realm again). Now I just need to pull it off with a character who got to the demon realm without talking to Emmindor so I can see whether the moonbridges will get deactivated or not.
On a side note: "walking" down the huge vertical wall at the Demon Realm is completely safe and doesn't even scratch the character, but then I tried to "jump" down out of curiosity - BLAM, 184 HP and 11 Athletics insta-dead. So don't jump down if you try this.
Edit: added pictures to show the place where I climbed from three different angles. You can see the green dots on the radar indicating the positions of Galdryn and Shaduroth (I didn't kill them because I just wanted to test whether it's possible to get out of the demon realm at all).