Samuel L. Jackson still thinks Mace Windu survived his electrocution and massive fall on Coruscant in Star Wars: Episode III - Revenge of the Sith. The actor has shared that particular theory before, but this time around it was in response to anothe theory, one that fans have posed: that Mace Windu survived, and became Supreme Leader Snoke, the shadowy big bad of the sequel trilogy introduced in Star Wars: The Force Awakens.
"I'm not a part of that rumor or theory," Jackson told ET when asked about Snoke. "I would like for Mace Windu to just be Mace Windu. I'm of the idea that Jedi can fall from enormous heights and still survive. The fact that he cut his hand off is not a big deal [either]. There are a lot of one-handed Jedi or Jedi with robotic or enhanced hands in that world. So hopefully I can be one of them."
Jackson is still interested in returning to the role of the Jedi with the purple lightsaber, though under what capacity would be up in the air. Some of the "Star Wars Story" stand-alone films, launching with Rogue One, do take place in the interim between Episode III and Episode IV, so nothing's impossible.
As for Supreme Leader Snoke, it seems nearly every character in Star Wars history has been theorized as the character, so much so that Lucasfilm Story Group member Pablo Hidalgo had a mug made for him that says "Your Snoke Theory Sucks" in a little tongue-in-cheek joke. Hidalgo and Star Wars: Episode VIII writer/director Rian Johnson have both been pictured with stickers with the same phrase, as well. Some of the more popular theories have included Ezra Bridger from Star Wars Rebels, the aforementioned Mace Windu, and even the Emperor's former master Darth Plagueis. By all acounts, these are all wrong.
Most likely, Supreme Leader Snoke is a new character created for the sequel trilogy. There have been a couple characters introduced in recent canon novels like Star Wars Aftermath that are actually solid candidates to eventually become the new Emperor analogue, though nothing has been anywhere close to confirmed yet. We won't find out until at least Star Wars: Episode VIII who Snoke really is, and what his backstory may be, when that movie hits theaters December 15, 2017.
But for now, we can be fairly assured that Mace Windu is not the culprit, at least as far as Samuel L. Jackson is concerned.