i believe if ron did become hb or quiddich captain it would have nothing to do with the mirror dd says
"it shows us nothing more or less than our deepest most desperate desire of our hearts..............................however this mirror will give us either knowledge or truth "
so it is impossible for the mirrors reflection to come true unless ron does become hb & q captain that would be entire coincidence
I wonder, because I can't remember, did we ever find out what Dumbledore REALLY saw when he looked in the mirror? I know he told Harry about the socks, but wasn't it implied that wasn't really true?
It might have been mentioned since, but I can't recall.
And I still doubt it, Dumbledore was quite specific about the mirror not showing the future. Now Ron would really, really want those things, but I'm not really sure he has what it takes to get them... I mean, he has been quite patchy at Quiddich in the past - I find it easier to believe Ginny would become captain before Ron. And I can't imagine the new headmaster/mistriss choosing Ron as head boy over all the other possible contenders. And beside, if Harry isn't in school, I don't think Ron and Hermione will really be there either.