The league would have real trouble fining the Pats, ordering them to stop, etc. They do have one effective tactic in response, however -- release damning information about the Pats.
Of course, if they don't
have damning information about the Pats ...
Actually, what I really expect that is them to hint in leaks that they have unspecified damning information, while sniffing that they're taking the high road, unlike the somewhat understandably tantrum-throwing Pats.
This could get good. Eventually, the press will figure out that if the league really did cover anything up for the Pats around Spygate or whatever, they'd be leaking it now. So if they aren't, there's nothing to leak!