IMHO, that seems more likely than seeing his family whole again. But if that's what Dumbledore were to look for, he would find it. Remember what Dumbledore said about the mirror--how it imparts neither knowledge nor truth. He could be 'vindicated' by the mirror, but it would be a false vindication.
You’re right, he would have seen it. I reread the King’s Cross chap. last night. ON pg.719 it says “At last he knew what DD would have seen when he looked int the Mirror of E. and why DD had been so understanding.....So obviously he looked in the mirror and did find out who killed Ariana. The answer may have been hard for DD.
but it would be a false vindication....
True! Now that makes sense. Thanks