I am sure that someone who has been sitting on the forum for years cannot leave just like that. The fact that Pakhitheboss turned out to be so mean in his promises and did not pay the debt did not prove his "innocence" (although it would hardly make sense) but says only one thing: he has more accounts. History shows how people who have received negative tags cling to their accounts "with their teeth." Here the situation is different, but lies always come to light; sooner or later, such people lose everything. I hope the same will happen to the rest of Pakhitheboss's accounts.
I've been following this topic for quite a while and seeing it updated made me wonder if he ultimately replied. I agree with you, those who have one and only account wouldn't leave like that. Whether we (publicly) accept it or not, high ranked Bitcointalk accounts (Sr Member+) can generate decent sums of money. From my experience through the AI Report Thread, a large number of those who were tagged for AI and had their posts deleted left without a trace (see Yatsan), never logged in again. Someone who's a Hero Member or Legendary doesn't abandon their account that easily, they'd apologize, beg, or find excuses in an attempt to save their account.
Someone who doesn't, is certain to have multiple accounts flooding the forum. As @Shishir99 already mentioned, people will find ways to avoid being found, and we've already discussed how it's possible. We're only relying on the possibility of them making a mistake and someone noticing it. Thus, the probabilities are quite low, but still possible. On top of that, even if we evidently track increased activity from other accounts, in the same region with Pakhit and see similarities, I don't know if it's enough evidence to accuse them, even if we all know that it's him. On the other hand, it might make it a little more difficult finding a signature campaign.