Yes in the short term we would struggle if Rooney were to be injured, but the formation and tactic would be changed and we would adapt. For example if Ronaldo was still with us Rooney would not have scored so many this season, Ronaldo went and we have a new focus, Rooney. Now if you take Sir Taggart out of the game that's when we will really come up against it.
The scientists or maths experts would say that luck has nothing to do with anything, probability is the real issue here. Scholes is obviously a better player than Vokes therefore Scholes is a better bet, even on a scuffed shot. I could go on and talk myself into a cul-de-sac on the merits of luck, probability and chaos theory, but I won't. United have more quality for most of the the time and that's what counts. As for the title I agree with Sir Taggart, Arsenal have a great chance of taking it. But only if they are lucky...