LeGarrette Blount and Brandon Bolden, who excels on special teams, are going to be on next year's roster. There will be one pass-catching back; whether that player is Shane Vereen or James White or someone else remains to be seen. If Stevan Ridley is re-signed, that's four running backs. There will also be competition from Tyler Gaffney, a 6-foot-1, 227-pound back who spent his rookie season on injured reserve. So Gray will probably have to prove himself in the offseason.
Vereen, who had 11 receptions in the Super Bowl, is a free agent. He probably won't cost the team a ton (for reference, Danny Woodhead got a two year, $3.5 million contract from San Diego in 2013).
The Patriots let Woodhead walk because they also had Vereen, so their decision may be based on their depth at the position. If they feel confident that rising second-year pro James White can fill Vereen's spot, you might not see No. 34 in a Pats uniform come next fall.
Part of Vereen's appeal is that he plays in a friendly system, but he lacks consistency, even in PPR formats. The team's willingness to re-sign Vereen will likely come down to price.