The easy short term answer is Braun.
Long term is trickier, as I personally don't think Braun is a well rounded enough sports entertainer to be the guy. Though he could very well prove me wrong.
But there are plenty of possible candidates. Dean, Seth, KO, Drew, Elias are all possibilities.
And of course there's nxt.
Losing a top guy and needing to fill that void is nothing new for the WWE. They will be fine.