If he erodes in the final two seasons of his deal his dead cap is entirely manageable at $4M vs. $14M in remaining salaries... Or if they chose to reduce his double digit cap hits in 2013-2014 by adding $4M or more in converted prorated salaries to his backend amortization. That final year has no existing amortization.
You could also make a case for spin purposes over the long haul that Mankins over the same 7 year contract span as Evans didn't total or average as much (because he played under the tender, and a reduced one at that, during the first year of Evans 7 year deal).
You can always find a way to spin or structure or manage a contract to rationalize it suits one or more legit purposes. He's certainly a Patriot for the next 4 years and can be one for the next 6 years if he remains a top performer and continues to represent value. If not, sayonara could loom in either 2015 or 2016.
Brady's deal as an alternate approach example is light on signing bonus but heavy on rolling guarantees for everything from roster bonuses to workout bonuses to season salaries that begin to lock in not only for skill and injury but for cap concerns earlier and earlier making his 4 year extension all but fully guaranteed. An indication they expect him to complete it, and a hint that they would have no trouble extending it by prepaying him some of what is guranteed $$ either way...
I do find it odd that Brandt keeps focusing on signing bonus as cash over cap as if it is some new wrinkle to the CBA. It has always been allowed, always been used or abused, and only fell out of favor a tad of late because of the Vick and Lelie rulings and several have nots choosing to rely on the cap to pay guaranteed money they didn't have the cash to cover via signing bonus. The owners now have clear cut recovery language concerning signing and other bonus nailed down in this new CBA. And teams have had some time and will have some more under a new revenue model to get their finances in line before the cash floors begin to impact them in 2013-2016.