There's a pretty straightforward campaign playbook for this sort of thing. Give the story to a relatively friendly reporter, match it with an interview casting it as youthful errors and a subsequent reckoning/remorse/growth experience, etc. Set aside whether this is an accurate portrayal in this case. If that story would have come out, matched with an interview with Romney explaining how he was a bit of a bully as a kid but then learned the error of his ways, I doubt very much that story would get a lot of traction outside of folks really determined to dislike the guy.
Again, not saying it should or shouldn't be a story; I'm saying I suspect it wouldn't, if for no other reason but that people give a big big benefit of the doubt to things a 65 year old man did when he was 16 or 17 years old.
(My own thought is that the fact that the campaign didn't try to handle this on its own terms probably tells us something about Mitt's own perception of it -- namely, that it's not a problem and not something that requires any explaining.)
Now, though, Romney's in a pretty different position. He first said he didn't remember these incidents. But his subsequent answers suggest pretty clearly that's not true. How are you sure you didn't think the victim of the attack was gay if you don't remember the attack in the first place. That doesn't make any sense. And the campaign's subsequent response has amounted to a messaging version of pleading nolo contendere.
My own sense is that the story is mainly damaging to the extent that Romney does not seem at all credible denying any memory of it -- and that dishonesty jibes with the general attitude that this are youthful pranks.
So my question is: Can Mitt put this behind him without some reckoning that he remembers that it happened?