Sidious purposely told Anakin that he was a Sith lord. Considering the level of planning that goes into everything he does, do you really think that he would risk his life on something like that? He was obviously either expecting or at least allowing for the possibility of a confrontation and must have had little to no doubt whatsoever that he would survive it. Otherwise he wouldn't have told Anakin anything. My guess is that he knew that he couldn't possibly sack the Jedi Temple unless Windu and the other high-ranking masters there were taken out first.
Sidious never puts himself in a compromised position. In ROTJ he had troops waiting for the Rebels at the bunker and had Death Star 2's main cannon ready to fire the whole time. Sure he was killed by Vader, but that is one thing that he really couldn't have planned for if you ask me. Now Mace defeating him in a duel that he purposely set up? That can be planned for.