According to the Rule of Two, what happens if the Master defeats the Apprentice in a challenge?

Question

By the Rule of Two, the Sith Order is strengthened when the Master has taught all he can and the Apprentice has surpassed the Master. It is the Apprentice's duty, then, to challenge the Master in a duel to the death as the final trial: the Master is to fight with his utmost to test the Apprentice's readiness to replace him, and if the Apprentice is indeed ready, the Master should submit to lay down his life for the Sith Order.

What happens if the Apprentice fails to defeat the Master? Is the Master duty-bound to kill the Apprentice as a duel to the death requires? Why? What if, as almost happened to Darth Bane at the very beginning, there's not enough time to raise a new Apprentice to full potential? Would sparing the Apprentice (albeit with some major punishment) be detrimental to the Sith or is it a case of "better than nothing"?

Answer 1

All indications are that the Sith Master will kill the apprentice and take on a new one. That said, the Master has absolute power and can theoretically choose to spare the apprentice's life in order to avoid having to start all over with a new apprentice.

Canon

The best canon description that I'm aware of regarding how the Rule of Two functions is:

Soon after destroying the Jedi, the Emperor had told Vader that he would one day be tempted to kill him. He’d said that the relationship between Sith apprentice and Master was symbiotic but in a delicate balance. An apprentice owed his Master loyalty. A Master owed his apprentice knowledge and must show only strength. But the obligations were reciprocal and contingent. Should either fail in his obligation, it was the duty of the other to destroy him. The Force required it. Since before the Clone Wars, Vader’s Master had never shown anything but strength, and so Vader intended to show nothing but loyalty. In that way, their mutual rule was secure. Perhaps Vader would attempt to kill his Master one day. Sith apprentices ordinarily did. They must, if they were trained well. An apprentice was unquestioningly loyal until the moment he wasn’t. Both Master and apprentice knew this.

_{Lords of the Sith, p. 27}

This quote makes it clear that it was the duty of the Master to destroy the apprentice if the apprentice showed disloyalty. The quote also makes it clear that the apprentice was expected to show disloyalty at the moment the apprentice challenged the Master. Taken together, this seems to be clear evidence that the Sith Master would destroy the apprentice if the apprentice challenged the Master but was defeated.

Legends

There are much better descriptions of the Rule of Two in Legends, and in Legends we have access to the thinking of both Darth Bane and his apprentice -- the two Sith Lords with the best understanding of the Rule of Two.

Darth Bane was resolved to kill his apprentice, named Darth Zannah in Legends, if she confronted him and failed, even though it would leave him without an apprentice and a failing body:

[Bane thinking to himself] An apprentice had to earn the title of Dark Lord, wresting it from the Master in a confrontation that pushed them both to the edge of their abilities. If Zannah intended to challenge him only after he was crippled by illness and infirmity, then she was unfit to be his heir. Yet Bane was not willing to initiate their confrontation himself. If he fell, the Sith would be ruled by a Master who did not accept or understand the key principle upon which the new Order had been founded. If he was victorious, he would be left without an apprentice, and his failing body would give out long before he could find and properly train another.

_{Dynasty of Evil, p. 11}

Darth Zannah also thought that Darth Bane would kill her if she failed while challenging him:

[Zannah speaking] The Master will train his apprentice in the ways of the Sith, until one day she must challenge him. If she proves unworthy, the Master will destroy her and choose a new apprentice. If she proves the stronger, the Master will fall and she will become the new Dark Lord of the Sith, and choose an apprentice of her own.”

_{Dynasty of Evil, p. 153}

It seems clear that the Rule of Two required the Master to kill the failed apprentice even if the Master was in poor health, and this comes from the two Sith Lords best acquainted with the Rule.

Answer 2

Not sure if this is the answer you are looking for but...

The Sith are very evil. This means that they won't respect or honor each other, they are together just because one of them is useful to the other (for a while). Don't expect a fair duel between a Sith master and his apprentice. Here is what you can easily find in the movies:

• Darth Sidious (Palpatine) killed his master (Darth Plagueis) when he was sleeping.
• Darth Sidious lured Anakin Skywalker to behead his apprentice, Count Dooku.
• Darth Vader killed Darth Sidious by throwing him away in pit when he was not paying attention on him. [Ok that in this case, the motivation was very different.]

Scavenging information on Wookieepedia about previous Sith lords, you will also find a lot of information about (1, 2, 3, and probably many others). However, since Disney's Great Purge, they lost credibility.

Generally, a Sith apprentice just do not duel his master directly. Instead, he elaborates a plan to kill his master by the hands of other people or perhaps attack him directly when there are few to no possibility of the master to defend himself. Also, the master may to the same with its own apprentice if he judges that the apprentice is not good enough or if he finds someone else that might be a better apprentice.

Also, an apprentice may start to sketch a plan to kill his master when he has himself found someone else that could be his own apprentice, motivating him to take the place of his master. This is easily seen by both Darth Vader and the Emperor who wanted to recruit Luke as an apprentice (although this is perhaps not the best example, but surely the most widely known). Vader wanted to have his son as an apprentice to defeat the emperor and then rule the galaxy together as father and son. On the other hand, the emperor lured both Vader and Luke to duel each other, with the hope that either Luke is proved to be unworthy and defeated by his father or that Luke defeats his father and became his new apprentice.

Answer 3

Your view on the rule of two is slightly skewed The Master will NEVER submit to the apprentice the battle is to the death no matter what so if the apprentice loses he dies The master will not hold back once the apprentice challenges the master he had better be ready or he dies that's the whole point the master is going to be ticked off he has just been betrayed by the person who has been loyal to him for who knows how many years now he knew it was coming but he does not want to dies so he gives it everything he's got and most of the time it isn't enough the apprentices are usually pretty smart about when they strike but if their not the the Master will find a new apprentice to train.