I'm convinced that between the 23rd and 27th of May, Van Gaal will be sacked and Mourinho will be named as new manager the same day.
My version of events:
Dec 2015: At some point during this period the board decide that Louis' goose is cooked as United manager. It may have been after we lost to Wolfsburg to be knocked out of the CL but more likely after losing three straight League games, which not only meant we would fail to challenge for the title for the third successive season but also meant CL qualification was in serious jeopardy. It had become clear that the team were not going to improve under his management to the level required and to allow him to continue into the last year of his contract would be unforgivable from the fans' perspective if these performances continued into next season.
At the same time it is decided that Giggs will not be the next permanent manager. This was only likely to be an option if things improved under LVG and if we were playing attractive football which would warrant continuity. As it was, it looked as if the next manager would have a very difficult assignment and Giggs has done little to inspire confidence that he is up to the task.
The club could not risk a third misjudgement, and as such, would only consider a very short list of names. One of the top names had just been missed with Klopp going to Liverpool so the club were keen to act quickly in securing any of the others that were available.
Mourinho is sacked by Chelsea on the 17th and it seemed inevitable over xmas that a deal would be done. I truly believe it would have been done in December if on the 20th Bayern hadn't announced that Ancelotti, another on the list, would be their new manager, meaning that Guardiola, probably top of the list, was available.
I think everyone knew that he was lined up for City but the fact it hadn't yet been announced probably gave United a slim hope that a deal may be possible.
The club was probably divided between support for Mourinho and Pep but with all the narrative at the time of United needing to play attacking football and all of the recent fallout from Jose's demise at the bridge I think we probably made an approach for Guardiola.
Mourinho feeds to the media and the club that he is ready to get straight back in to management to try and land himself the job before any contact is made with Pep, but the club wait on Guardiola's decision meaning that LVG survived into January.
Jan-16: At some point in January we are probably briefed that Guardiola to City is done as everyone suspected. It is confirmed on Feb 1st. Mourinho is now the obvious choice.
However, the timing is not good. LVG has just won at Anfield. We're at the end of the transfer period and changing managers so late would appear foolish. We also don't want to be seen as responding to losing out to City on Guardiola. Mourinho is less keen to step in right away having been made to wait and not having the opportunity to improve a depleted squad. So we continue as is.
Feb-16: In February I believe we make a verbal agreement with Mourinho for him to start in the summer. We make payment to him to prohibit him from signing with another club before June 1st.
Mar-Apr 16: The rise and rise of Pochettino at Spurs leads some at the club to believe he is a better fit for United than Jose. However, majority view is that Mourinho is a safe bet and it would be wrong to pass up on him again. Plus Poch would be difficult to attract and acquire.
United make the Cup final, guaranteeing LVG will see out the season, meaning the announcement will be made in the last week of May. From LVG's comments to the media it would appear that, if a deal has been done, he is unaware of it, probably thinking that because he survived the worst spell in December he has weathered the storm.