Best thing that could possibly happen this off-season is NBA teams telling Carsen they will draft him first round next year if he comes back and averages 6 assists.
The NBA drafts on athletic ability and potential. He would likely not gain much in draft stock if he came back and improved in every facet (and would likely lose ground, since he'd be a year older). In the NBA draft, two birds in the bush is worth more than one in the hand.