Well Pep Guardiola isn't going to retire from his coaching duty anytime soon, and yes he would arguably be the best coach in football history, he did not only perfect the art of winning games and winning competition many managers before him has done something very similar coaches like Ancelotti is an example but Pep Guardiola did it in such a fantastic way, he doesn't play to win by packing the bus but his plays sweet football like the Tikitaka.
Pep Guardiola is an excellent coach who Manchester City will never have again. I'm not sure, but I don't remember Manchester City ever winning three trophies in a single season before. Guardiola broke a record there, so any coach who takes over will know he is an excellent coach. He is just as intelligent as Real Madrid coach Ancelotti, but we cannot compare the two because in my opinion, Ancelotti is superior to Guardiola in terms of managing a team. Even in defeat, Ancelotti will inspire his players to keep going, and occasionally he will substitute players who are quick to score goals. If you watch a lot of Real Madrid games, you will notice that they consistently score goals in the last 90 minutes of the match.
Ever since he took over as Real Madrid's coach, Ancelotti has always supported his players even when they make mistakes. However, Pep Guardiola lacks that quality. In a video I saw following the Chelsea vs. Manchester City match, Guardiola was visibly upset with his players because he didn't think Chelsea would play that way with them. Being a good coach means that you will never lose your temper with your players, and even if you do, you should hide it from them because it will affect how they play on the pitch.