If Mace Windu is alive, he could prevent Luke from making some of the mistakes he made in the original story. His wisdom and experience as a Jedi Master could guide Luke better, and maybe they could form a stronger Jedi Order together, faster.
His survival might mean that the Sith's plans are thwarted earlier. Since Mace Windu was one of the most powerful Jedi, his continued existence would be a major threat to the Empire. He could inspire more people to rise up against the Empire, changing the balance of power much sooner than in the original storyline.
Mace Windu could have trained new Jedi in secret, creating a more organized and powerful resistance against the Empire. This would have forced the Empire to divert more resources to deal with the Jedi threat, potentially weakening their hold on other aspects of galactic rule.
One possible plot could be that Mace Windu survived his fall from Palpatine's office. He could go into hiding, secretly training new Jedi in the ways of the Force away from the Empire's reach. He might discover ancient Jedi secrets that could help in the fight against the Sith.
In such fanfiction, it could lead to a completely different power dynamic in the galaxy. Maybe the Jedi would regain their prominence and prevent the rise of the Empire.
Mace Windu was a powerful Jedi Master. He was known for his purple lightsaber and his skills in combat. He was a member of the Jedi Council. He played a significant role in the Clone Wars, leading the Jedi in many battles against the Separatist forces. He was also involved in the discovery of the Sith Lord Palpatine's true identity, which ultimately led to his confrontation with Palpatine in the Chancellor's office.
Perhaps Mace Windu survived and was captured by the Empire. He manages to escape during the events of Star Wars Rebels. He then teams up with the Ghost crew. His presence would be a huge boost to their morale, as he is a powerful and well - respected Jedi. He could also help in the fight against the Inquisitors, using his skills to outwit them.
Well, it could focus on Mace Windu's early days in the Jedi Order. Maybe show how he was trained, his first encounters with the dark side threats, and his rise within the Order.
He could be a Force - ghost. His spectral form could guide Kanan or Ezra at crucial moments. For example, when they face a difficult decision regarding the Dark Side, Mace Windu's Force - ghost could appear and offer his wisdom based on his own experiences with the Sith.
Another possibility is rogue Jedi who have turned to the dark side. They could be former comrades of Mace Windu, and he has to face them in combat. This would add an emotional layer to the story as he has to fight people he once considered friends and allies.
One of the most memorable moments was when he faced Palpatine. His purple lightsaber clashing with Palpatine's in that intense duel was epic. Another moment was his leadership during battles in the Clone Wars, where he showed great strategic acumen.
If Mace Windu didn't die, he might have trained more Jedi and prevented some of the Order's downfalls. His presence could have altered many events in the galaxy.