Palpatine is without a lightsaber, and defeated. Windu still holds his lightsaber, but decides he's not going to arrest Palpatine, he's going to kill him. Anakin stays at the Temple, trusting in the Force. Windu beheads Palpatine. The Jedi then seize control of the Republic, purging the Senate and the courts, as Windu and Yoda agreed to do shortly before Windu learned about Palpatine's true identity. Would that have been the right choice? Is it really that much different from Anakin striking down a defeated Dooku, or Luke almost striking down a defeated Vader? Would Mace Windu, and perhaps the most of the Jedi Order with him, have fallen to the dark side and remained in control over "their" "Republic"? Or was it really the right thing to do, given the extraordinary circumstances... or would it have been the same as when Palpatine was giving emergency powers to deal with the Separatist crisis?