The Jedi Master's lessons gave meaning to Anakin's existence, setting the example of what a Jedi could, should, and must be. Vader's memories of Qui-Gon Jinn vindicate the belief Luke Skywalker would come to hold: that there was still good inside Darth Vader.
He'd heard Qui-Gon's voice in the desert, begging him to listen to his better nature, not to give in to his hatred. He hadn't listened. At the time, he'd told himself he was imagining it, but he knew he was lying. If Qui-Gon was out there, somehow, Anakin owed him an apology.
Would Anakin have been good if Qui-Gon trained him?
It's obviously speculation, but I'm going to say that Qui-Gon would have managed to keep Anakin from falling to the Dark Side. Anakin's core problem was that he wasn't a good fit for the Jedi Code. Anakin was a very passionate person, and he wasn't able to suppress his emotions and remain detached.
Qui-Gon Jinn FINALLY Reveals His Feelings About Darth Vader - Star Wars Explained
Who is stronger Luke or Qui-Gon?
Though Qui-Gon Jinn was strong in the ways of the Force, including telepathy and levitation, there's just no way he would beat Luke Skywalker in a fight.
He was also well-versed in ancient Jedi prophesies, and thus suspected he was living in the time of the Chosen One. It's gradually becoming clear he was the one Jedi who could have actually stopped Palpatine. E.K. Johnston's new book Queen's Peril has just supported that assertion.
Qui-Gon was ultimately defeated by a move that can only be done with a double-bladed lightsaber as Darth Maul used the handle of the weapon, striking Qui-Gon physically on the chin, stunning him for just long enough to deliver the killing blow.
Though Palpatine regarded Vader with the caution common in a Sith Lord to their apprentice, he nevertheless entrusted much of his plan to Vader's abilities. He even referred to the broken man as his friend on numerous occasions, though he still found himself betrayed by his apprentice during Return of the Jedi.
What would have happened to Anakin if Qui-Gon lived?
Had Qui-Gon lived, however, he would have become the father-figure Anakin so desperately needed. The bond between Qui-Gon and Anakin would have been far greater than simply master and apprentice; they'd practically have been father and son.
Qui-Gon believed Anakin was the Chosen One, prophesied to bring balance to the Force, and that their meeting was no accident. He brought Anakin to the Jedi Council on Coruscant, and was angered when his fellow Masters refused to train the boy, but saw their lack of vision as only a temporary setback.
The book then digs into one of the final scenes in The Phantom Menace, where Anakin watches Qui-Gon's funeral pyre blaze and “feeling a profound sense of loss.” After leaving his mother and the only home he's ever known, Anakin then experienced intense battle and the loss of a person who promised him a better future.
Ahsoka Tano is technically more of a Gray Jedi than a traditional Jedi, but her prowess in lightsaber combat could have allowed her to defeat Vader. In Ahsoka and Vader's duel in Star Wars Rebels, Ahsoka sliced open Vader's mask to reveal part of Anakin's face.
It's worth noting that Qui-Gon may have beaten Maul if he had more training in fighting opponents with lightsabers. Until then, most of the Jedi in the Order believed the Sith to be extinct.
Vader remained loyal to the Emperor in the year that followed, feeling that he had to remain loyal to his master due to the power of the dark side of the Force.
Qui-Gon Jinn, although idolized by viewers, may not have been right in everything he did and could have been the reason for the fall of the Jedi Order. George Lucas believes Anakin should never have been a Jedi, and Qui-Gon's recklessness in wanting him trained led to his fall to the dark side.
What happened to Qui-Gon's lightsaber after he died?
After Jinn was mortally wounded, Obi-Wan Kenobi used it to defeat Darth Maul. The weapon would become the temporary lightsaber of Kenobi until 28 BBY when he constructed a second lightsaber identical to his first one that had been lost in the duel with Maul.
More cunning and devious than all but the most attuned Force-sensitive beings, Darth Bane could more than likely defeat Yoda in a battle of both strength and wit.
Dooku was powerful and extremely skillful with his lightsaber, to the point he easily beat Anakin and Obi-Wan. Still, Dooku was less powerful than both of his masters – Darth Sidious and Yoda. The Battle of Geonosis set Palpatine's ultimate plan in motion, and it is considered the first battle of the Clone Wars.
These factors combined seemingly indicate that Star Wars' Darth Plagueis was more powerful than Palpatine, although the latter's ability to manipulate others gave him a significant edge over his Sith Master.
When Qui-Gon was killed by Darth Maul, Dooku was so saddened that Qui-Gon's death lead to Dooku's transformation into the Sith Lord Darth Tyranus. He would later provoke the memory against Obi-Wan Kenobi, Jinn's apprentice.
To summarise: Master Yoda could not warn the other Jedi about Order 66 because he did not know about it until it happened. He knew the Jedi would die, just not how or when the blade would drop.
