If your DS did not have a Principal nom, but the candidate from your district did, then yes, your DS goes to the NWL. Each MOC has 1 spot/year, except for that rare year when a 2nd spot is open (because there are only 4 class levels; maybe someone left mid-year or prior to graduating, etc). The odds of getting an appointment have bounced around on this forum (anywhere from 50% to 75% chance getting an appointment off the NWL). I think it's closer to 50%, but don't know the actual number. Until your DS receives the TWE he is still competing. Hang in there, and he should make sure he has Plans B, C, D lined up just in case.
Also, USNA admissions stated on FB that all candidates would know their status by 15 APR.