The Carolina Panthers were interested in offensive guard Kevin Boothe, but that door is now shut as he returns to New York on a one-year deal, according to a report from Kim Jones. It's likely Dave Gettleman could only offer a one-year deal at max anyway, so why would Boothe come to Carolina vs. staying with the Giants? In terms of a pure talent upgrade this is the first strikeout the Panthers have had this off-season.
With the free agent market drying up, there are a few decent guards left. Jake Scott of the Philadelphia Eagles is still available, but fills more of a left guard role. From there you have a rash of guys who underperformed on bad offensive lines -- Matt Slauson (Jets), Leroy Harris (Titans), and Deuce Lutui (Titans) are all still available, but would be incremental upgrades at best.
It will be on the Panthers to find the players they need through the draft. Chance Warmack is a first round possibility, while there are several second round prospects who could solidify the RG spot.