If he's saying the truth will eventually come out means that the truth is not out yet .
But you're right, he's too vague.
well I took that truth will be out part as "proven without doubt" because what each sides believes to be truth is already out. We just don't know what is the actual truth for a fact. In other words for example "your truth" is that it's Malachi on these songs but it's not "the truth" as it's not established or proved as fact and accepted by everyone.
It's a bible verse actually that's in full form is "Then you will know the truth, and the truth will set you free."
given that this person was asking for closure and saying stuff like "fans need this" he's saying that when you know the truth all of these will be over and you will be free of all these doubt.
but it can mean in either way. definitive proof in both scenarios - whether it's Michael or not - would bring closure.