All depends on what the Devils have in Hrabarenka, Helgeson, & Mozik - if one of them can step up and show they deserve top 6 minutes like Severson did last year, maybe Gelinas becomes expendable. If not, you wait and see how guys like Gelinas, Moore & Merril do under Hynes and re-evaluate in another year when these guys have some more experience at the NHL level (one of them is likely to be the 7th d-man, plus injury call-ups) and potentially Santini is ready to compete for a spot.
I don't think you go looking to deal any of these young defensemen until you have to.