I guess it would depend on how much information and evidence you gave the IRS. The easier you make it for them to investigate and file charges or issue a deficiency, the more likely the IRS will do so.
If the IRS believes that you have valid non-hearsay information and that you can be a crucial witness to the tax evasion, don't worry as they will be contacting you
The information provided in this answer does not create an attorney-client relationship and is not considered to be legal advice.
They almost always take what seems like too much time on cases like this, and VERY often will not contact the reporting person. There is nothing you can do.
This is not intended to be legal advice, and is general in nature.