It's not good because decision tonight means enrolling early at FSU on Monday. Delaying, taking an OV to South Bend next week means he would not enroll early at FSU but could enroll early at ND because classes there start 1/18
Either way, he effectively needs to make a decision tonight. As you said, if he doesn't show up to classes on Monday, he is probably coming to ND.
I feel for the kid. I know what it is like to make life changing decisions having left good jobs twice (hopefully each time for better jobs). Good news for me is that I didn't have to make that decision at 18 years old.