Ziyech wouldn't fit this Manchester United. He needs to be in a team that presses forward rather than one that just sits back leaning on the counterattack. As someone else said some time ago; Klopp's Liverpool would be a much better fit for him (yes, I know in some way Liverpool is also a counterattacking side, but in a much different way).
Besides this, I'm eager to find out where he'll go and how he'll do. He's one of these guys who can be a great success, but he could flop as well. Before this season I thought he would maybe be a good fit for a club like Sevilla, but not a bigger club. However after what he's shown in CL this season I'm not sure he can't do it at a higher stage. He delivers against any opponent. Bayern, Real, Juve, he can cope. However he definitely is the type of player that needs to be with the club that fits him, a manager that trusts his abilities and plays a system that suits his abilities. He will never flourish in a Mourinho team for instance. Some players can do it in any system or tactic (De Ligt for instance), but Ziyech's success will depend on many factors. However he's shown this season that he can cope at any level.