Pep Guardiola may have made the decision to leave Manchester City for reasons that perhaps cannot be explained to the public, so Pep Guardiola prefers to look for other reasons so as not to make Manchester City's condition worse. It is possible that Pep Guardiola will return to Chelsea and improve the condition of this team to get into the top ten again from the top of the standings.
I don't think Pep Guardiola will manage Chelsea if he leaves Manchester City. Of course it doesn't make sense that he got everything with Manchester City but chose to leave City to join Chelsea. If you pay attention to Pep's coaching history in two different leagues, of course his next step will be to leave that league. He left Barcelona and did not coach another team in Laliga and also he left Bayern Munich and did not coach another team in the Bundesliga and it is very likely that if he left Manchester City he would not coach another team in the Premier League.
Pep Guardiola really appreciates the fans and he doesn't want to betray up on coaching another team in the same league. Yes, it is very likely that he will go to another league after his contract end with Manchester City or he will stay with Manchester City for a long time. Many say that he wants to return to Barcelona someday and it could happen.