FACTS SUPPOTING HIS SURVIVAL:
-ROTS did not specifically mention, nor show Windu's death, it only implied this. The Jedi as well, do not discuss the fact that he died. They seem to forget it.
-In the CW animated series, he was able to jump and fall extremely high distances.
-In AOTC he was able to do the same (ending CW battle)
-In AOTC, the Jedi (Anakin and Obi-Wan) were shown to be able to slow themselves when falling, and grab on to nearby objects. They both had a method in which they slowed themselves, by fully extending their bodies, to slow the fall
-Mace was considered one of the greatest jedi next to Yoda, not just some regular jedi, but more powerful than most.
-Mace had learned to master the force and fighting so well that he created his own fighting style, Vapaad. This fighting style was a balance between the dark and light sides. He was one of the few who could master it without falling to the dark side. This is what allowed him to go up against and nearly defeat Sidious by himself. Without Anakin, he possibly could have defeated Sidious. Whether sidious was simply faking his defeat when Anakin walked into the room is still unknown, however.
-He could have possibly went into hiding, reallizing the threat the empire posed to the jedi, and knew what would happened if he returned. He could have went into hiding and become one of the Jedi who hid and were on the run from the empire in the lost years between ROTS and ANH. Windu could have been killed during that 19 year time period, only the future EU works will reveal this!
FACTS AGAINST HIS SURVIVAL:
-The ROTS novelization states clearly that Mace did in fact die.
-He does not appear in any later episodes, or in the rest of ROTS for that matter.
-He has yet to appear in any official in-continuity Expanded Universe works.
-The Jedi as well, do not discuss the fact that he died. They seem to forget it.
-Mace, in just a few seconds had his fighting arm cut off, was shocked with force lightning, went through extreme pain due to the force lightning, was likely very shocked mentally that he had been shocked physically by force lightning and had had his hand cut off, and finally, he was thrown far out a window into the coriscant traffic.
-Being thrown into traffic, Mace ran the risk of being hit by a vehicle, or quickly crashing into a close object before being able to save himself through the force and using the special powers he had been shown to have.
Despite his great abilities shown in the official canon, Windu was overtaken by the combination of the sith lord, Darth Sidious, and the soon to be sith lord, Anakin Skywalker. Windu could have likely survived without Anakin's intervention. Through extreme shock and pain he was thown out a window. At this point, the debate beins. Yes, based on official sources he died. All except one. Now, the movie never explicitly says that he dies. It only implies it. So, it never says he does or doesn't survive. It leaves it ope. However, according to the levels of continuity, the movies take precedence over the books. Well, since the movie never says "yes, he died" or "no, he didn't die," the book does. The book answers that question. It says he dies. Since the movie never says. The book does, it says he dies. Since it says that, he did. storywise, continuity wise, he did. And since he is no longer mentioned, nor does he return anywhere in continuity, and could have been killed easily from falling, due to several reasons listed previously, his demise is even more likely.
Sadly, Lucas chose to follow the movie cliche of having the black man die, but in this case, that had to happen due to the story situation. Of course, Windu could have been reincarnated as Mace Towani. He could have wanted his name to be mace to reflect his past life. And, well, the ewok movies he was in take place after episode III, so, you never know! But that is another discussion!