There's nothing wrong with just having an MC as ST, Fabregas played as a false nine for Spain at Euro 2012, on such a huge stage. It's fine to have a player slightly out of position, United sometimes have Rooney and Welbeck on the wings and Carrick and Valencia have played in defence where Carrick was a liability, so the reduction in performance is a good reflection of this.

For the injured player not being replaced, I would agree if it was a serious injury. If just a light knock, I wouldn't agree so much, but we are not informed about the severity of the injury during the match.