Has this been discussed as a possibility?
Let's say that Tyus is told that there's a 90% chance he will be picked in the top part of the second round and that he believes this.
But, as part of the feedback, he is told, "There's a possibility that if you go back to school that next year you may end up in about the same position (Say a 50% or 60% chance of Early second round and a 40% to 50% chance of being taken at the end of the First Round).
"Tyus, these teams would be drafting you on your athletic potential and mental and physical toughness. They know you are not yet a finished product. But becoming a marginally better shooter or passer in one more year at SU isn't going to change your draft position all that much."
The reason Tyus would not fully enter the Draft this year believing he would be a early second round pick would be the potential for being a higher pick in 2019.
If that isn't likely to happen, then the smart money approach would be to go this year.