I won't try to tell the student what to do, but I will say: (1) Doing a PhD and anything else at the same time is pretty exhausting, and a pretty sure recipe for dragging for PhD out for a long time. A PhD requires a lot of dedication. (2) When you're trying to decide between the two options, think about what you'd rather have 30 years down the line. You can always start another company once you've got your PhD; once you've worked for a few years, will you be in a position to go back to graduate school?