It's only guaranteed if he makes it to the major leagues (at least to the point of making things worthwhile). The washout rate for 1st rounders in the MLB is much higher than any other sport, so there's a good chance he never plays in the majors. Plus he would have to earn close to league minimum for several years once he made a MLB roster, and maybe even deal with being Kris Bryant/Ronald Acuna'd if he's actually any good. Not to mention, he could always try his hand at baseball a la Tim Tebow if he stinks at football, and he might just like playing football more, even with the CTE stuff.