Ok. I wrote a petition and asked for GM help. Sadly to no avail. Even the GMs cannot discard deadlocked quests nowadays.
In effect, this probably means no more quests for Garbald, because you never know when a new quest might lead to Vladovic and get stuck there too.

I am really amazed how a developer who knows that his system is buggy can remove the only means to get around this bug. In light of this I find it hardly convincing, that it was done to avoid exploiting. I mean, who is more important to the game? The player who loves playing and wants to test more quests or the exploiter, who will be bored and gone soon anyway?
I liked many of the new quests. A lot of of hard and good work went into all the wonderful new stories. Sad, that this is now all wasted on Garbald. And yes, I know that I could do all the quests with a new character. Hey, in fact the exploiter can do so too and will have no problem with it. But if I do it, it would not be Garbald doing it and the stories of the adventures would not be his to tell at the fireplace in the guild hall.
Well, sorry for this rant. I really don't want to start a new flame fest and this topic has surely been beaten to death before, but this needed to get out. The disappointment was simply too much. I will now be quiet and let Garbald go back to mindless mining and looting, to earn gazillions of Tria, so our guild can perhaps with a lot of luck afford a hall, where Garbald will not be able to tell of his new quest adventures at the fire place.
* Garbald slaps himself. "Quiet! Bad Garbald! Be constructive!!" Garbald silently walks to a dark and hidden corner in the deepest part of the dungeons and weeps. *