Spoiler ahead:


After Radovik's death i decided to defend Vernon and co. against Dijkstra. However, upon killing Dijkstra the game locked me in the theater and wouldn't trigger any conversation or whatever was supposed to happen. Instead Vernon and the others are just standing there and the Quest still tells me to kill Dijkstra and his followers despite them being already dead. I already tried reloading the last checkpoint but it always ends like this.

Repair/update your installation...

I guess that worked, because the client did download something. However, the last Checkpoint before the fight was still broken and now Dijkstra just stands there and does nothing. I tried an earlier savegame and was finally able to finish the quest (Dijkstra still wouldn't attack, though).