A lot of talk here that Miller is leaving. He said in his instagram story last week that he is staying, but "people leave based on their situation" being a guy from the inner city, it wouldnt surprise me, but I think Franklin will be in his ear.
With that being said, I dont see any Juniors leaving. Next year Boobie has a chance to be on many of the preseason watch lists, and one of the best backs in the country.. which will ultimately up his draft stock.
One of the issues is the NFL draft slotting. In 2018 a kid picked in the middle of the first round (15) got $8m. The 45th pick, Josh Jackson, is making $3.6m and the 75th pick is making $2.6m. Assuming you get six years, which is the average NFL career (outside of QB's) you will probably never make that money up.
My point is, if you get paid $8m in the first year versus $2.6 you lost $5.4m. Probability says you will never make that up in a six year career. Plus, the team is invested in your success. A third rounder brings no real investment (GM/Coach isn't being fired if 3rd round pick doesn't work out). So, if you expect to be a third rounder after your jr. year but a first rounder if you stay through your senior year, that is probably a better investment (plus, get insurance!)