While there is definite chance that a person will be charged and "can do time" for any kind of government agency fraud, what this person is looking for is something we do not have and no one on a message board can provide for them. And that is tell them what are the "chances of prosecution and how much time the person is likely to get." This OP is in contact with the person who did turn them in, and they're sitting there waiting and speculating about what the agency will do, how likely they are to face charges and if so, how much jail time they're going to get. That's just too far from the picture. The one thing that no agency is going to do is provide feedback to the people they've received information from, and those who've reported fraud about the outcome of their investigations.
If they find out whether the person was charged and how much time they got, it won't be because of any cut and dried formula from the internet, or any feedback they've been given by the agency. One thing that people on the outside of an agency do not really have any conception of is how many cases are being investigated in any time period, how many of the cases investigated will actually be prosecuted, and how much actual jail time is given to people who are determined to have committed welfare fraud. If every single case of fraud was prosecuted to the fullest extent, there would be NO room in our criminal justice system for any other criminals. If the person is willing to make reparations, there's a likelihood that they will be able to work it out with the agency through repayments and sanctions.

