What must be worrying to Rosberg, is that they keep talking about "tailoring" the next chassis to "suit" Michael.
That generally means no one else can drive it.
And the lingering doubt for Team Mercedes must be that, having "tailored" the 2011 car for MS, they discover he really is over the hill, and they dwell somewhere in the bottom third of the results list.
If I were looking for an ascending German driver, I'd be tempted to buy Sutil...