I guess we'll have to see really. For me Cahill has always been so important for the simple reason that for so long we where dogshit in anything but a 4-5-1. With centre midfielders like Carsley, Neville and Osman and Gravesen that was expected, lets be honest.
I remember watching us after Cahill got injured in 06/07 and the introduction of Manuel Fernandes. We saw glimpses of what we could do then in a 4-4-2 which contained a midfielder who was potentially an all rounder. Obviously Manny's injuries problems and consistency always made it difficult for us to do it week in week out.
Now we have Arteta, a player who has been a breath of fresh air in the middle. Defending, attacking, controlling our play and most of all keeping our shape. His a disciplined [Poor language removed], maybe a bit too disciplined for his own good at times. He can do a bit of everything and with the right partner (potentially Rodwell maybe) we could play in any formation and Cahill absence wouldn’t hurt us anywhere near as much.
I also think there will come a time when Moyes should be looking to get rid of this withdrawn striker/target man and go for something and provides a lot more control. Maybe a 4-3-3 like Barcelona. Three midfielders who face the play and pass and move, that’s the way forward in my opinion, the way to truly dominate and control a game.