If it is thrown out on a technicality, that still leaves the issue of City's image being tarnished. The solution should be either:
a) Sue for damages wherever possible, explaining why the allegations were false to a real court, a panel that decides a verdict by the facts laid out, rather than the outcome dictated by secret(or not so secret) allegiances with connected entities(G14).
b) Counter the Der Spiegel articles with the truth laying out exactly where they lied/made mistakes. Pay a top journalist to come look at it and take him through what all of it means.
Some people will still ignore it even if City prove it but as long as enough sensible people, who's heads aren't up their own arses accept the truth when they see it, it will slowly but surely erode some of the damage done.