There is no way Ronaldo will consider returning to Manchester United after his previous experience that led to him moving to Saudi Arabia. I also think he will rather accept a move to Sporting than return to United, and with the way things are playing out I think he might even retire at Al Nassr.
What if returns as a coach or sporting director, what will you say?By the way, he loved Manchester United so much that he risked his reputation with the club by going on air and criticizing on how Manchester United is being mismanaged and why things have to change. So who knows? You could see Cristiano Ronaldo in the Manchester United dugout one day.
I don't think Ronaldo will ever become a coach. He would be rather the guy who owns part of the club or become the president and do more things in the background. His lifestyle and all the entrepreneurial projects he has make it unlikely that he would work as a full-time coach. Of course nobody can know it for sure, but I doubt he is the kind of guy who would want to work 365 days a year as a coach.
There is also this wrong idea that every great player can be a great coach. Look at Maradona, he was so bad as a coach. Ronaldo has all the top qualities as a player, knows where and when to run and how to execute everything on the field. But I don't think he is a strategy guy like Guardiola. He is also not like Zidane or Ancelotti.
President is more what resembles him. He could boss around a bit and he wouldn't have to be dealing with daily issues like a coach has to.