Depends on how it was done. The only way I could see it happening is if Ambrose or Rollins, or probably both of them, turn on Reigns and join Evolution (reports say that one idea that's been suggested for the breakup of The Shield is to have Ambrose and Rollins both turn on Reigns, eventually), leaving Reigns to fend for himself all on his own, which he is obviously more than capable of doing.
It's a good idea in theory, but I'm not sure I'd care to see it executed on the show because it would require Evolution to stick around as a group a lot longer on-screen, and I really don't care to see them "ruling" the show like it's 2003 all over again. And hell, back then, at least we had Smackdown as an alternate brand that we could watch and be entertained by if we ever got bored of seeing Raw centered largely around Evolution, but we don't even have that today, leaving us in a situation where we'd be forced to watch both Raw AND Smackdown largely center around Evolution 2.0. No thanks. A short-term reunion to feud with The Shield is awesome. Seeing Evolution in a prolonged role (that stretches to at least a year or beyond, for example) is not.
I think the breakup might come when Ambrose costs Reigns the match against HHH at Summerslam. Why he does it, what kind of tension occurs between him and Reigns (and/or him and Rollins, or between all three Shield members) that builds to it, etc., I don't care to speculate on at the moment. But that's what I could see plausibly happening.