The league should be fine with it. I'm a little surprised the MLBPA would be ok but I haven't and can't do the Present vs Future value math right now but I would bet the present value, and the value over the next 10 years compared to the following 10 years means the dollar amount is not insane. I messed around with it a few days ago and had figures like $37M = $70M in 10 years.
But on the surface getting $20M for the next 10 years, then $680M in years 11-20..... not outrageous to me. The question to ask is what is the value in years 1-10 compare to the corresponding years 11-20? I.E. Value of a year's in 2028 vs 2038. In the year 2038 he'll get paid $68M. We've been saying this since 1975, 'In year X, $YM will seem like peanuts".