#2 Keep Mourinho now and sack him at the end of the season
Top coaches are a rare commodity and an even rarer commodity in the middle of a season. Manchester United board have been in this situation twice in recent memory and they have acted in two different ways.
David Moyes was sacked four games to the end of the season. Louis Van Gaal was allowed till the end of the season and he even won the FA cup at the end of that season but was still sacked. In Jose Mourinho's turn, the Van Gaal precedent may be the better option to follow.
Jose Mourinho can be allowed to try to salvage this season. A top-four finish is still mathematically possible but highly unlikely. They are still in the Champions League and can win it.
Their round of 16 draw against PSG does them no favours there. The FA cup is another trophy they can lay their hands on. All in all, they are still in three competitions and can mathematically still make the top four.
The sack at the end of the season is because Mourinho is the wrong fit for Manchester United. He does not play the United way, neither does he possess the style, charisma and affability required to be the boss of one of world football's biggest clubs.