The restaurants aren't open 24 hours a day.
Room service is, and he can always eat in the cabin. But the roon service menu isn't grand.
The buffet is open more often than the restaurants. Some NCL ships will have a food court mall fast food cafe, which is open 24 hours a day on some ships. He shouldn't go hungry for long.
Hint: When the restaurants are open is posted in the Freestyle Daily, so look at it to find out when what is open.