Basically, he needs to look at his goals.
Northwestern is a good enough school that he won't really be screwing himself by going there; if he has a lot of interests outside the law, he probably wouldn't be terribly happy working 80 hours a week at an super prestigious firm anyways, so he doesn't really *need* HLS.
That said, he might really *want* HLS. If so, the money shouldn't matter, and he should go there. This decision shouldn't really be based on the finances, rather on what will leave him most satisfied. If he wants to go the biglaw route, he's already decided that his happiness over one year is worth 140-160K to him. If he'll be happier going to HLS, then it's easily worth the cost in loans.
On re-reading, I feel like I'm saying he should ignore the scholarship; I don't think that's the case, just that he should be basing his decision on whether or not to take it on other factors in addition to the debt.