Many who are following this story have weighed in with their predictions on how the Supremes will rule. So I'll pick up the challenge and go where angels fear to tread.
The prevailing view seems to be that LaRue will win a split decision, with a condition. The condition is that the Court does not avoid the merits issue by holding that the complaint was technically deficient. I think that's unlikely. The court will reach the merits and will rule, 8-1, that LaRue's claim can go forward. Why? First principles. In the first year of law school we were taught that there should be no wrong without a remedy. There seems to be no dispute that LaRue was wronged, and there's no disagreement that if he loses he will have no remedy. In the upside-down, inside-out Wonderland of ERISA law there's no guarantee that common sense and simple justice will prevail. But this one seems too clear-cut for the Court to deprive LaRue of a remedy through a technical reading of one of the few simple and clear provisions of what is, in general, a bizarrely complex statute.
The lone holdout? Chief Justice Roberts.
One more thought. The defendant made the all-too-predictable argument that a finding in LaRue's favor would open the "floodgates of litigation," swamping the federal courts with 401(k) investment decision cases. Enough already. It won't happen, but even if it does, the system can handle it.