Take this with a grain of salt, but my guess is that the board on some level has to judge him as being so high performing that they would try to keep him as long as that doesn't cause too much PR damage to the company, or the deals get them in too much trouble with the government.

This is just a total guess, but I assume what a lot of the board want is for him to sell as much to China or indirect channels as he can get away with. So whatever these deals were that involved this woman, they probably want him to get those deals through it he can get away with it (although they wouldn't admit it).

I see this more or less as Huang doing his job. And relative to international expectations at that level of wealth, one public affair is probably not something most of the board (presumably largely male) is going to (privately) judge him for.

So if the board is investigating, I assume what they are trying to figure out is if the US government is going to do anything (probably not) or waiting to see if there is going to be some kind of public demand for him to be removed. Or it there is something likely to come out that will cause either of those things.