I think you can hire an agent now and still go back. From an SI article from 2019: "Under the new rules adopted by the NCAA's board of governors and Division I board of directors, college players are
allowed to be represented by agents who are certified by the NBPA and NCAA (the agents must become NCAA-certified no later than Aug. 1, 2020) after any season, so long as they request an 'evaluation from the NBA Undergraduate Advisory Committee.' They must end the relationship if they return to school."