Which is an issue with the NCAA’s byzantine rules, but…
The NFL now works to provide all juniors who declare for the draft with an assessment from a third-party scout, advising those players as to when they can expect that they would be drafted (or if they would be drafted at all).
Now, if the player receives a “fifth round or later” grade, and chooses to not believe it (“I’m better than that! I know I have first round talent!!”), that’s a different issue.
Regardless, all the rule is doing is preventing a college junior from playing football in his senior year, if he declares early (granted, if he’s on a sports scholarship, he’ll undoubtedly lose it). It’s not preventing that player from going to college at all.
You don’t lose NCAA eligibility by declaring for the draft. You lose it by hiring an agent. Players are free to go through the draft process unrepresented and retain their eligibility.
Does the NFL still have its service where scouts employed by the league would tell prospective players what round, if any, they’d likely be taken in? That certainly kept some young men in school who really needed to be there, and it would be a shame if they had to fall back on agents’ word only.