Lewis will likely be the guy who sees the majority of snaps so long as he is healthy. White has shown he's deserving of some snaps as well, and Bolden remains as an ace special teamer and a guy who can be trusted to do simple things.
The replacement would have to be for the Blount or Jackson hammer role. Among likely free agents, Lynch, Foster, Ivory, Forte, Ridley, and Morris all fit that mold, in descending level of preference. Foster, Forte, Lynch, and Ivory all have proficiency as pass catchers and protectors, too, though Foster and Forte are by far the best of those.
Whoever they bring in, and it could very well just be re-signing Blount, will likely be for low-rent. As evidenced by Belichick allowing Blount and Ridley to leave and replacing Blount with a guy who hadn't played in a year, it's clearly a role that, while important, doesn't have a huge price tag attached to it in this offense.