It's definately doable, there is enough work between Ronnie and Ricky to warrant keeping them both. On normal rushing downs, I'd imagine Williams and Brown would continue to split carries.
I think Ronnie Brown's skill as a reciever and blocker are key, and what I think would be the big selling point of keeping both. He's got the ability to play other positions then runningback.
Ronnie Brown very well might be a player Miami might want to look at playing split wide occasionally like Brian Westbrook or Marshall Faulk. He showed some pretty good hands this season, and made some one handed catches and adjustments to badly thrown balls.
When Bill Bellichick talked about Ronnie Brown in his pre-game conferences, he really seemed to think Ronnie Brown has alot of ability as a reciever. Here, look at some of these quotes-
http://www.patriots.com/search/index.cfm?ac=searchdetail&pid=13839&pcid=85
"He has good speed. He can get to the corner. Outstanding hands. Excellent. I'd say as good of hands as probably the top five percent of all backs. He catches the ball easily. He gets turned up field in a hurry."
http://www.patriots.com/search/index.cfm?ac=searchdetail&pid=13791&pcid=85
"I'm not saying that you would want to play him at receiver because it would be a little bit of a waste, but I think he could play receiver because he has the hands, the quickness, he has enough vertical speed that he would really be a problem out there. Kind of like an Andre Johnson kind of guy, that is just a big, fast, strong and just hard to deal with."
Brown's also got the ability to play as a fullback on passing down. He can stand up and take on defensive ends and blitzers, and he even managed to eliminate bigger defensive linemen with some forceful use of the cut block.
If Ronnie and Ricky are going to stay and be utilized correctly, we're probabaly going to see a more rush heavy attack with Ronnie playing more of a hybrid role.
