As we all know Anakin Skywalker a.k.a Darth Vader was Sith Apprentice under Sith Master Darth Sidious (Palpatine). They operated under the Rule of Two, meaning that Vader would have to kill Palpatine to inherit his title and become new master.
Vader of course killed Palpatine, but in the process was mortally wounded himself and died minutes later. Nevertheless, although Vader supposedly rejected the Dark Side and turned back to the Light in the last moments of his life, we never saw him formally abandoning Sith Order or Palpatine's teachings. This is completely opposite to the scene in Revenge of the Sith were he knelt before Palpatine and almost ceremonially pledged himself to said teachings.
Therefore, my question is: did Darth Vader die as a Sith Lord (at least technically) and was he actually the last Sith Master to ever exist, effectively ending the Order not by killing Palpatine, but by dying himself without training an apprentice? I would not discuss theories that Luke could be his successor, effectively continuing both Jedi and Sith in one person, because this seems far fetched.
Anakin becomes Vader: