I suppose if you're already in Paramedic school, or at least have gotten accepted and just waiting for class to start and don't otherwise need your NREMT to renew your state EMT while in school and are going to immediately get your NRP after you graduate medic school it'll probably be fine. But then again, there's always the chance you don't finish medic school for X reason, or life throws you a curve and find out you have to move or whatever....like everyone else says, it's just too easy to keep NREMT current until you get NRP (can't imagine any reason to keep NREMT current once you get your NRP though, but keep it current to you get your shiny new medic card).
I (foolishly) let my NREMT expire a couple years ago as I had no plans to move out of state then, and then I was thinking "Well I'll just go to medic school this year and simply get NRP and not worry about NR EMT...." well now I have a conditional job offer for an out of state agency that I will definitely be accepting (assuming nothing stupid happens to revoke the conditional lol....but hey, that's Murphy's Law right? so now I'm kinda kicking myself for not renewing NREMT, and the process to regain it for having been expired so long is kind of a pain....so yeah, my vote is keep your NREMT current until you have your NRP....though I would say if it's already expired and you're already in medic school then don't worry about it so much, but hey, stuff can still happen....