I'm gonna reply my best. I just watched the scene and if Anakin didn't stop Windu, sidious would have died because sidious was trying to sweet talk anakin so if anakin didn't kill Mace, mace windu would have killed him with the killing blow. Watch the scene
Nice necro, and your wrong. Sidious would have killed Windu, Anakin didn't kill Mace he just disarmed him. Mace's saber was actually bending and he was losing his grip on his saber, regardless of Anakin being there or not, Mace would have been killed.