If Xabi can win either Bundesliga or Europa League, it's better for Manchester United to hire him and kick the bald guy. Manchester United already lose their legacy as one of toughest team in Premier League. They need to find a good coach who can able to develop the whole team, just like Xabi who wasn't sign many players, but he develop the existing players with a new strategy.
I don't know why but I feel Xabi to Leverkusen seems hard to me. Xabi has just started at Leverkusen and no doubt United is a big club but I feel he might want to continue a bit more years at Leverkusen before going on to manage some big clubs. As for United also, there will be lot of other experienced candidates in priority before Xabi on the list so even if he is on the list someone else might replace ten Haag if board is thinking of sacking him. Xabi does have qualities but situation at United needs someone big and experienced who can build up a huge squad well.