I would say it's a near certainty. The way the NFL views RBs, it's best to start the clock on your rookie contract as soon as possible in hopes to get that 2nd contract.
Chances are he is going to be around a 3rd rd pick making around 1 mil a year on his rookie deal. He doesn't stand much to gain by staying. RBs rarely are given a 1st rd projection, and if so, its becuase they have some sort of physical trait that makes them freakish. Staying in college and padding stats might make Sampson a 2nd rounder, but you risk injury and are a year behind the clock. That and NIL would have to pay him close to an NFL salary, which for a RB, isn't happening.
So, yes, even if he loves Knoxville and his heart wants to stay, I think he will be councilled to declare.