The only manager to win 3 consecutive PL in the last 30 years or so is SAF.
Not winning the league this year isn’t the end of the world for Pep. He won’t get sacked.
But this is a turning point, Pep left Barcelona and Bayern saying he was burnt out and that he couldn't reach the players anymore, but the thing is both boards thought they could win without him, and didn't really trusted his method in the long term.
I don't see this about sacking him, this is a crucial point for both him and City, if he truly has lost the dressing room there's two options:
Plan A is the usual, swap the manager and see if he can lit a fire on those players like Mourinho has done with Tottenham, then after 2 or 3 years sack him because the same thing happens again
Plan B is the one I'm most interested to see, if the board back Pep, they keep the same method and get rid of underperforming players it could start a long term era for City & Guardiola, something that truly has a page in football history, it could also end up being a huge mistake for all parts.
And recently, Zidane has proved that you don't really need to rebuild a whole squad to make them hungry again, I'd love to see for once what Guardiola is able to do in a 5 to 7 year span with a DOF that follows his instructions, it may be the last chance we get before he goes to hunt silverware with PSG, then Italy to win a easy Scudetto with Juve and retiring to coach young players for Barcelona.