Hopefully he will have improved a lot on the mic by then... which judging by the two recent interviews he's done via satellite lately, he hasn't.
I'm not a Reigns hater, but he just isn't gonna be ready to headline Wrestlemania and fight Brock Lesnar by the time March gets here. Their original goal was to have him feud with Triple H so that Hunter could help make him look like a star by the time he even won the Rumble, but at this rate, that feud will be forced to happen later and Reigns will be going into the Rumble pretty cold. They'd have to do some really magical booking to make him look like he's ready in such a small time. It's not impossible since they accomplished that same thing with Batista in early 2005 (he went from being a plain midcarder to being the #2 over babyface in the company within a few months, and him vs HHH at Wrestlemania 21 earned more than a million buys, in case anyone wants to question the success of that feud), but I don't foresee that same thing happening here with Reigns.
I wouldn't ignore the possibility of a Ryback/Goldberg type build.
Suppose Reigns comes back in December and proceeds to squash jobbers, possibly two at a time.
If he continued this on each broadcast, it would build him as an indestructible force on a mission.
He can win the Rumble, but instead of feuding with Triple H, he continues to squash jabronis.
If he defeated Triple H too soon, people would see right through that as typical WWE bullsh*t.
However, if he gets support the way Ryback/Goldberg did, he will have earned it physically, not politically. Once he defeats Lesnar then he can feud with HHH.