Biggest question: if he doesn't go to LSU, will there be a bigger meltdown than there was for McKnight?
Honestly, it depends. Meltdowns mostly depend on how the recruit handles the process. By most accounts, McKnight was pretty much always a USC lean, but sort of strung LSU along and gave the fanbase hope... to the point that even some of the national recruiting "experts" thought he's choose LSU. I don't know exactly why he strung LSU along, but I don't think he ever truly planned on choosing LSU since he openly talked shite about LSU and Larry Porter (his main recruiter, if I remember correctly) after it was all said and done. The meltdown was a result of the last second rejection... though I'd say he clearly planned to reject us all along. It would have been much less if he committed to USC earlier in the process and simply and honestly stated, "Sorry, don't want to lead you on; my heart is just set on USC."
Similarly with Landon Collins last year, he planned on Bama, LSU swayed him, then the girlfriend put the screws to him in the last couple days leading up to the All Star game announcement till he capitulated to her and went Bama. I don't think Collins was a bad kid at all. Had he simply remained a heavy Bama lean and not had his last good visit to LSU and given so many people hope he'd choose the Tigers, the meltdown wouldn't have been nearly as bad... fwiw, I believe he honestly did decide to go to LSU; it was clear to those who followed closely that this caused a spat with his girlfriend and she put the screws to him till he re-chose Bama.
Bottom line, if it comes down to the last week or so before signing day and Fournette chooses elsewhere, there will be a meltdown. How big that meltdown is will depend on how he handles things... as well as how successful LSU is on the field this coming season. A great season will lessen the blow.
To the poster who mentioned vision: I agree. Forgot to mention that in my earlier post. He really does a fantastic job of keeping his head upfield scanning the defense for a seam to run through.