It's hardly Greg Hardy-level negotiations, but the one missing (but available) starter from the 2013 Panther defense is in negotiations - NT Colin Cole.
Cole started 13 games for Carolina, a mild surprise when the starting duo had been billed as Dwan Edwards (who started the other 3 - the first two, and the season finale) and rook Star Lotulelei. Star and Cole switched roles at times, but Cole played mostly NT, leaving the massive Lotulelei to make more plays. Cole only played 30% of snaps, however, giving way to Lotulelei and fellow rookie Kawann Short for more playing time (not coincidentally, this pairing was far more effective than any other pairing against the run; Cole had some struggles, and Edwards is not a good run defender)
Now 33, Cole would have nine years experience coming into the year. The deal is expected to be near the minimum.