Let's say you're the race director of some small time marathon. This isn't your full time job. Some delusional megalomaniac cheats in your race, but then promotes his accomplishment and its downstream effects with such fervor that he has no choice to be hold his line. Since it's obvious to anyone that he's guilty, you DQ him.
Now since he's all in on this baloney (he can't let his kids think he's a fraud, for crying out loud; he could even get fired!), he sues for defamation or something, who cares if it's baseless. Do you have time for that BS? Is such a hassle worth it to maintain the sanctity of the sport?
I suspect that the RD will just let him go. A thousand people on the internet will buzz around Rossi's every move for the next two years like a swarm of angry hornets; you don't have to be the public face at which he can thrash wildly in his doomed defense.
I do suspect that Boston will take a tougher stance with him for future qualifying, requiring a legit time from a better regulated race. And Rossi will either go one of two ways: stop running competitively and let time bury the story or try to train obsessively in order to retroactively clear his reputation with some future performance. If he runs 1:34 and 3:21 next year off 60 mile weeks, that 3:11 won't look so absurd anymore.