I expect us to move to two centre backs now, on paper. Daley Blind / Michael Carrikc will be anchoring the midfield, shielding the defence and even dropping into the defense to push the other two centre backs out wide, which will launch our full backs. This is similar to how City does it, with Fernando having that midfield role, frequently launching both full backs at the same time.
On paper it will look like we've made a major switch, but in reality we'll be where LvG always wanted to be with our three centre backs. We've just been missing the right players to do it, on account of injuries.
As far as I can see, the only really big change would be if we switch to more traditional wingers, but with the signing of Falcao I don't see that happening at all. We will retain the shape we've been working on from ahead of the third centre back / midfield anchor, with Di Maria and Herrera most likely first choices in the "normal" midfield roles, and Mata / Rooney playing ahead of them, depending on whoever is fit to play up front.
What we've been doing up until now has mostly been down to lack of proper midfield and / or centre back options, depending on how you look at it.
So we'll be going from:
-----Evans - Jones - Blackett
Valencia - Fletcher - Di Maria - Young
-------------Mata
---------Rooney RvP
To something more like this:
----Evans - Jones
Rafael - Blind - Shaw
---Herrera - Di Maria
--------Mata
---Falcao - Rooney
The only actual change is that we're sacrificing one deep laying midfielder for a two way midfielder, and I would assume that this has been LvG's plan all the way, we've just been lacking a Carrick or Blind, and proper midfielders for the strategy.
Of course we're very short on players who can have that two way role in midfield, with only Herrera and Di Maria doing it properly, so if any one of them are out I think we'll revert back to what we've seen so far, pushing Blind or Carrick into that spot, and adding another proper centre back in their stead. This could also be an option against top sides, where we might want to go with a more defensive minded approach.
As for width, it doesn't have to be a problem. Just look at Liverpool who actually played with a quite similar shape to what I've outlined above against Spurs, and City did the same against Liverpool. You just need proper movement, and that's what we've been lacking so far. Di Maria and Falcao will both help tremendously with that.