Why are you trying to punish the player even more? Isn't it enough that he (probably) will get his winnings confiscated?
I'm not trying to punish him. I'm highlighting a mistake he made, not in doing anything against the terms but in giving himself a rod for his own back. In fact, he appears to have done two silly things:
1) Self excluded.
2) Changed bet size in a potentially nebulous area.
You don't need to self-exclude to stop playing. Just uninstall the software. Again, you're creating a potential problem. Of course, if he wants to, so be it. But why take the chance of running into issues with sister casinos? since he's not a problem gambler, there is nothing to gain and potentially everything to lose - as we're now seeing.
He can change his bet size if he wants to, and if the casino then says "hey, you broke the terms by increasing your bet size with a bonus in play", he can come back with "but the bonus wagering was complete, show me the logs to prove I broke the terms", at which point the casino might provide selective logs which don't help, at which point the player can say "hey, these logs are wrong..." etc. etc., until such a point that the whole thing collapses in confusion. Or he gets paid - maybe.
The alternative scenarios as per my suggestions would be:
1) Uninstall the software already. Don't self-exclude.
and
2) Play the bonus, finish the wagering and cash out. Don't look to tempt fate.
In the future, I hope he follows my suggestions. I won't labour the point further.
On the face of the evidence here, and regardless of these two rather calamitous matters, he needs to be paid.