Well the article above is an example of what could happen overseas, where much of the ATC system is not in control of the government.
Here in the U.S., it is hard to say as it would depend on what exactly happened. If a controller intentionally did it they would likely lost their job and face criminal charges along with prison time (nowhere is that explicitly spelled out but it is the likely case).
If there was no intent to cause what happened then it can get rather complex as the entire situation is taken into account. A controller in a worst case scenario may lose their job but it is not a guarantee that they will. More likely, the controller could be decertified, be required to go through a skill enhancement training session (or sessions) and become recertified on that position before being allowed to work that position on their own again. They may have to testify in court if it goes that far as well. Many many other things could happen and it's hard to even lay out what might happen as the situation in which the accident occurred is taken into account.
But there is no "three strikes and you're out" system or any other system in which a controller is punished that is used... at least that I'm aware of.