The person who is more likely to move on here is McCarthy, who should have at least some interest elsewhere and while there's a pocket for him here - Nemec and Walsh could easily not be in Utica next year - he is definitely going to be squeezed from both sides.
McCarthy is a superior prospect to Walsh, although he's not close to Nemec. That being said, McCarthy is a completely different player-type to those two, so there is absolutely a need for him in the Devils system. Nemec has superstar upside, whereas Walsh projects to being a better-skating Will Butcher-type. McCarthy's upside is to become a Siegenthaler/Marino-type (not saying he'll be that good, of course), which is to say a strong defensive presence who also skates well and handles the puck capably. The Devils don't have another RD close to NHL ready to fill that role, so McCarthy would certainly be a guy the Devils would want honing his game in the AHL.
It also bears mentioning that McCarthy is friends with Jack Hughes. This would certainly not be a sole reason to sign him, but considering all the other factors in play, it makes no sense for the Devils to simply allow him to walk instead of giving him an ELC and allowing him to further develop in the AHL.
Looking at the Devils RD pipeline, the NHL/AHL depth charts look something like:
NJ
1 Hamilton
2 Marino
3 Severson
UTICA
1 Nemec
2 Walsh
3 Blujus
Now, next year we can probably assume Severson -- on the final year of his contract with Nemec and Luke Hughes (left shot, but has played a great deal on the right side as well) knocking on the door -- will not be back. This opening would create a gaping opportunity which, for the Devils (lacking any other AHL-ready RD prospects as Casey is at least a year away and Leddy/Barabosha several years away), could only be filled by McCarthy.
As such, I would 100% expect McCarthy to play for the Devils organization next year. I'd say the RD depth chart is likely to look like:
NJ
1 Hamilton
2 Marino
3 Nemec
UTICA
1 Walsh
2 McCarthy
3 Blujus
I would also expect McCarthy to soon usurp Walsh as the top RD in Utica since, as I've said at length, he plays a more NHL-type game and is, to me, the superior prospect.
Solely based on points, Case McCarthy is now third amongst BU defensemen behind freshman Lane Hutson (Montreal) and senior Domenick Fensore (Carolina); both of whom are smaller players seemingly more suited to college hockey.
Any likelihood that McCarthy still gets signed or with the right-hand shot D drafted last year have the Devils moved on from him?
Absolutely 100% yes. See my above explanation.