#2 Mancini would have been sacked
Almost four years into the takeover by Abu Dhabi United investment group, City still had just one FA Cup to show for all their wealth. Heading into the final day of 2011-12 season, Mancini's future was by no means a foregone conclusion. Two and half seasons into his reign, patience with Mancini had started to wane; tangible success was crucial to secure his future.
In our story, having bottled their best chance at a league title for decades, Mancini would definitely have been sacked in the immediate aftermath of the disaster. It is not immediately clear who would have replaced him then – perhaps eventual manager Pellegrini would have taken over one year earlier (it is doubtful Guardiola would want to try his hand in the Premier League immediately after his Barcelona stint).
In any case, Mancini's position would have been untenable, and the club and the fans would bid him goodbye.