How high are these extra costs that the neighbor has gotten himself into?
Hard to say. The costs of the underpinning will be covered by the shell builder.
The procedure including the other costs is estimated to be between 4-8 thousand € without actually knowing.
I don't think the general contractor will cover it, no matter what happens he is definitely always the one liable, or he will have the work gilded.
Liability in case of damage will still pass on to the neighbor. In whatever form.
Has the new neighbor now seen reason, or have the fronts hardened even more?
No...he was pretty cheeky at times...also to the judge, who then warned him. I would say that he is mainly angry at himself. After all, we could prove how often we made him generous offers, for example before our construction started the deep foundation on his side.