Apparently so, as this article indicates.
Apparently there was some confusion within the mOO staff on the status of the rule change involved, even though I clearly remember reading the NCAA reminding everyone long before the May 29 deadline that currently underclassmen still must withdraw from the draft 10 days after the NBA Combine (the aforementioned May 29 this year) to retain their college eligibility. The rule change they were confused about
does not go into effect until the NBA and NBPA agree to the rule change in their collective bargaining agreement that will activate the rule.
From
NCAA notice "Flexibility for going pro and getting a degree" as Updated Sep. 20, 2018:
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NBA draft flexibility
College basketball players who request an Undergraduate Advisory Committee evaluation, participate in the NBA combine and aren’t drafted can return to school as long as they notify their athletics director of their intent by 5 p.m. the Monday after the draft.
This change is effective if/when the NBA and NBPA make an expected rule change, which would make undrafted student-athletes who return to college after the draft ineligible for the NBA until the end of the next college basketball season.
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The NBA and NBPA haven't agreed to that rule change yet.
Professional.
Returning to Mizzou not an option for undrafted Jontay Porter