From the most recent RAW Rant re: The Shield–"Shame they’re breaking up because they’re all coming into their own as workers and talkers." Isn't that actually the best possible scenario? Each of them becomes their own unique force and they have a great blow-off at Wrestlemania before moving on to becoming three upper-Mid to Main Event players?
Furthermore, imagine if they were one of the few stables to have a great blow-off without becoming diluted and/or limping around forever. A few years from now you could have some storyline that brings the three back together for a legitimate "grown men mark out" moment unlike every tedious nWo or DX reunion.
I'd be fine with swapping out Reigns and replacing him with someone from NXT like Adrian Neville, or ideally Chris Hero if he hadn't left, but it feels like there's still a ton of juice left in the original gimmick, much like D-X getting reinvented in 1998. Splitting them now would just leave Seth Rollins in no man's land, whereas if you spread it out a bit you can get two or three big storylines out of it.