Is that an absolute certainty that the funds cannot be retraced ?
Obviously the funds that were sent to Kexbui cannot be reclaimed ....but... if the person was asked to invest in previous exchanges (and made a profit) previously , is there not a way to trace these transactions ?
The funds can be traced, the problem is what do you do next!
First, you (the victim) must file a complaint with law enforcement, no exchange will act on just an email and some screenshots, they have no way of knowing which one is the true story, and they will act only when some official asks for an inquiry.
The problem is the time, by the time this will arrive the funds will be of course gone, most like the user on that exchange will be a fake one, and even if they were stupid enough to use a legit one you would still be faced with the trouble of filing a civil lawsuit against a foreigner that might not have a thing on this name so you have nothing to take even if you win the case.
That's the problem with those scams, by the time you realize it's a scam the worst is already done.
Of course, filing a complaint is the way to try to do something and if those pile up law enforcement might do something that at least will scare them but recovery of funds...slim chances.