Here's the issue...
Pesce was added last summer and seems to be in the medium-term plans. Kovacevic was JUST extended so is in the medium-term plans. Nemec or Casey or both are high quality prospects who will be in the NHL soon.
Even if you trade one of Nemec or Casey, that's 4 right handed D that should be playing every night. Nemec and Casey are waiver exempt for now, but won't be for all of Hamilton's contract.
2 guys are probably going, and Hamilton and one of the kids seems most logical. Hamilton within a year. The kid within 2 years.
Things could change with regards to Pesce or Kovacevic in 2 years though, I suppose. It could be both kids staying and one of Pesce / Kovacevic going (and Hamilton too).
This is the crux of the issue. Pesce and Kovacevic aren't going anywhere - one just signed as a UFA and the other just extended. If the Devils don't trade Hamilton, then Nemec is likely gone - hopefully traded for a young forward in a similar situation. Casey has a great attitude and could spend next season starting in the AHL to continue to work on his overall game and being the first injury call-up, then you re-evaluate the following offseason.