Actually, after giving it some thought, I don't know if Peterson's contract is really a problem. The reason? No guaranteed money.
If I read his contract right, all the money remaining on his contract is base salary. Now, it's very high base salary: $12,750,000 this year, $14,750,000 next year and $16,750,000 in 2017.
For the moment, let's look at that first figure. LeSean McCoy's contract with Buffalo would leave the Bills taking an $18,250,000 hit if they had to cut him this year. Next year, it would cost the Bills $13,000,000 to cut him. Now, his cap hit isn't nearly as high as Peterson's would be (if the contract stayed as is), but the risk is higher because of the dead money.
With DeMarco Murray, the Cowboys' concern wasn't his overall contract for $42 million, but his guaranteed $21 million for the same reason. Murray's dead cap for this year is $18,000,000 and his dead cap for next year is $13,000,000. If either of those backs hit a wall, the team is going to take a pretty big hit.
Dallas only takes a big hit with Peterson if he actually plays. Under his current contract, if the team cut him before camp for some reason, there would be no cap hit. If it paid him his $12.75 million for this year and he clearly was not the same runner he had been, then the team can cut him next year with no cap hit.
Now, we'd have to do some restructuring of other contracts to make that possible, but it's certainly not impossible. However, the Cowboys could also set themselves up for a more minimal hit this year by converting some of his base into bonus without changing the overall numbers. That would create some dead money, but if Peterson is everything we hope he could be, we could renegotiate the deal next year.
Neither is ideal, of course, because we prefer to get him for much less money, but I don't think his contract necessarily is a deciding factor in this ... I think it's compensation. If we're going to essentially "rent" Peterson for a year, then the cost to rent him (a second-round pick) is too high.