Never mind the questionable cause of action (fraud...detrimental reliance...???), his damages have to be entirely speculative. That's usually the part of an action that can make or break it (see, also: defamation/libel)
While I think Les has a valid expectation that he'd be a candidate for the Hall of Fame, I agree with you that damages could be hard to prove.
Would he be in the Hall? Can't say.
Would he be considered? I think likely so, just based on nominating criteria.
Maybe I'm wrong, but I think a lot of this is going to hinge on what LSU agreed/promised to do. That's where he maybe has some leverage but I don't think he has very much.
I feel bad for him. I tended to like the guy more than most banal coaches. I am glad he wasn't hired at AU as some speculated he might. Overall I think he's a fairly decent guy, but this makes him look kinda sad and pathetic.