It doesnt make sense to get rid of Mayo next year because of the big dead money cap hit --
http://www.spotrac.com/nfl/new-england-patriots/jerod-mayo/
The earliest it would make sense to move Mayo IF the reward was worth it would be 2016 where the dead money cap hit is only 2.4m
The Pats are going to roll over this year's extra cap money into 2015 anyways. So extending McCourty and Revis does not necessarily have to come at the expense of Mayo. In any case a base LB core of Mayo, Collins, and Hightower would put our best 3 LBers on the field. So all this talk of trading Mayo is premature.
If a couple million dollars would be needed to keep both Revis and McCourty, I think the more obvious candidate for trade/cut would be Amendola who is playing 3rd/4th fiddle behind Gronk, Edelman, and arguably Lafell.
http://www.spotrac.com/nfl/new-england-patriots/danny-amendola/