Oh boy will these be unpopular and controversial, but here we go
1. If Moyes was given time and funds to rebuild the squad, I could see us winning our 21st title instead of Leicester in 2016 due to the fact that it was such a low points tally finish (81) and every other top 6 club was struggling that year. That alone would've bought him so much time, though, that he probably would've managed to see out his original six year contract that ran until 2019. Now, I'm not saying that Moyes is a world class manager and he would've been the second coming of Ferguson, but I think we would've been in a much better place by giving him more time than the LVG & Mourinho disasters.
2. If we let Ronaldo join City in 2021 and sign no one / a midfielder instead, we would've finished third last season on around 80-85 pts and Ole would still be our manager. We probably would've signed Haaland and Rice, which would mean us challenging, maybe even winning the league this season.
3. Had we managed to avoid getting robbed in the CL in 2010 & 2013, we would've went to the final in both seasons, but probably would've lost to both José's Inter and Heynckes' Bayern Munich. We would've been CL runners-up in 2009, 2010, 2011 and 2013.
4. If Ferguson stayed in 2013, Ronaldo would've left Madrid and rejoined the club that summer and I reckon we would've gone on to win at least 2 more CL titles between 2013 and 2018.
5. We probably could've and should've won the CL in 2002 and 2004 but got upset by smaller teams in both seasons. I was too young at that time, though, so cannot say for sure because I wasn't even following football back then. But I've always got the impression that we missed out on 2 CL titles.