I think theymos probably knows satoshi's identity. Although it's quite easy to remain anonymous on the internet so it might not be true.
I see no reason why someone who appeared from nowhere on a cryptography board would ever let anything slip to anyone under any circumstances.
Well we could probably say the same for Ross Ulbricht

. I think it's relatively easy to remain fully anonymous if you set out from the start to do so, but it's also relatively easy to screw up just that once... or twice. Satoshi used tor if I remember correctly, but I'm sure there's ways that can leak your IP occasionally, or if the FEDs are controlling certain exit nodes maybe they can grab your IP somehow. You could further mask this though by using tor via public wifi, a proxy or connecting via a throwaway simcard. You can still screw up in other ways though, but if you're committed to privacy and remaining anonymous it shouldn't be that difficult. I think the biggest way satoshi could be discovered was if he was a person that was already public known in the crypto-sphere and his writings could be compared to that person, but if he was a relative nobody then that's pretty much impossible, and if he was somebody he would have probably been linked already.
What about destroying everything that is not in public view and end the debate ?
I don't think this should happen. As r1s2g3 said, it's possible (though not probable) satoshi could return one day and he may wish to find some information from his PMs (or maybe even delete it himself, but that should be left up to him). I'm sure satoshi was smart enough to not leave anything incriminating behind though, but even if he did then maybe fair game to anyone who did manage to get access to it.