There's no reason for Woger not to maintain his level that he supposedly found at the end of this season. Why but he takes his matches way too seriously. I don't think he'd be able to forgive himself if he didn't. His scheduels are especially designed that way and the favours he gets at Slams are also part of his success. So if he loses then it would be simply because he's opponents played better tennis on that day. The reason why he wasn't able to win a Slam since 2010 AO is not because he couldn't keep his level at the same rate, but because there were players better than him on those occasions and played better tennis to win those titles.
Not every match is on Woger's raquet - not when you have guys like Nadal and Nole around. Even Tsonga and Berdych are pure threats to him if they catch him early. Those matches will be on their hands to win or lose. Too bad Andy never got the chance to play him in the semis or earlier on in his entire career. That could have portrayed a different scenario by now.
The draws will be the biggest threat to all. And AO will probably want to go with someone that would make the most noise. They all want attention and money.
When you have won as much as Roger has you can afford to create a schedule that makes the majors your main focus. Tsonga and Berdych are always dangerous players, but Roger has since crushed Tsonga a few times including the US Open and hes taken good care of Berdych. the match against Tsonga Roger was 2 sets up.
Murray has never beaten Roger in a Slam as you rightly say both matches were in finals but no reason to think that a Semi or quarter would be any different, as Roger once said he is essentially an attacking player Murray is defensive, in that kind of match up the attacking player in this case Roger decides who wins the match, not the defensive player which is Murray.
Nadal is always a threat to Roger, but Roger when playing well is capable of beating him handily like he did at the O2, Djokovic is the only real concern but even he showed signs of fatigue towards the end of this season, how he starts 2012 will be very interesting indeed.