We're making a lot of assumptions here, but let's run with it. Maybe the NCAA isn't inclined to budge on the "100 mile" rule, and since ND is technically 106 miles away, we're on the wrong side of the law here. We might be able to get around that, but it would require putting some political pressure on the NCAA (or USC) via public statements from Kelly and/or Swarbrick.
That kind of politicking can be very high risk. If that's the issue here, Kelly and co. may have decided that Isaac would be nice to have, but not worth the effort.
But, if the only issue is administrative paperwork, bureaucratic phone calls, etc., then I agree that likely wouldn't slow us down at all.