I do not think Manchester City will sack Guardiola. Guardiola is the best coach in Manchester City's history. He transformed City from a mediocre club into the best club in europe. The team consistently showed great dominance in the Premier League. City also won the Champions League and FA Cup with the help of Guardiola.
Anyway, it is possible that if Guardiola fails this season, he will voluntarily leave Manchester City. Guardiola is only 54 years old. He will not think of retiring so soon. He will probably want to take on a challenge with a new team.
Guardiola's contract with City ends in 2027. So even if he fails, he may decide to stay at the Etihad until 2027. Whatever, I am pretty sure that Manchester City will not be the Premier League champion this season.
For me, it it were to be another coach incharge of Manchester City, he would have been sacked since last season. I think Guardiola is still the coach of Manchester City because of the respect the club has got for him. It true his the greatest manager of the club but he has to know and accept that eras comes and goes. I believe that if he doesn't get it right at least this season, he should step down honourable. Seriously, if this form continues and the club management is finding it embarrassing, he wouldn't have any option other than to sack him if he refuses to step down himself.