Considering that we have to shed salary before trying to re-sign the likes of Mike Wallace (UFA), Keenan Lewis (UFA), Rashard Mendenhall (UFA), Jonathan Dwyer (RFA), Isaac Redman (RFA), Emmanuel Sanders (RFA), etc. whether or not we are able to re-sign UFA Ramon Foster really says nothing about what the team truly thinks of the guy. With wunderkind guard DeCastro coming back from injury, there may not be enough money left to keep Foster next year (unless they can save some money by releasing Colon and replacing him with Foster...not sure what the dead money penalty would be for cutting Colon, though, so I'm not sure if that is realistic).
Despite being a backup, Foster has pretty much become a starter with all the games he's played. I suspect he wants and probably deserves starter money which we won't likely be able to pay.
With all the FAs, Foster is likely gone imho because someone else will commit to him as a starter.