I have heard Anakin kills Mace halfway to 2/3 into the film. When Obi finds Anakin Im sure he will tell him how crazy things have become and Anakin will agrgue and taunt Obi about what he thinks is right and wrong. When Obi tells him about Palpatine and that Master Windu was slain by a Dark Lord of the Sith Anikin will just give him a cold stare and say "I Know" as he ignites Mace's purple saber. The look on Obi's face would be priceless.