severance package disguised as a buy-out offer

I work for a newspaper and I found discrepancies in accounting. Several customers (large stores etc.) had credit balances and I was told not to bring it up. I was told another time that if I had any paperwork on the matter, that it would be good if it flew out the window.
The company claimed to have fixed the problem, but there are still major accounting problems.
I reported it to HR.
They offered me a "buy-out" that would equal about 4 months with 4 months of insurance. I was given the offer on May 15 with 21 days to decide but it states in the paperwork that it's effective May 31. (Only 16 days). I asked HR what would happen if I didn't take the buy-out, they said I would be terminated on May 31 anyway. This is a gift-wrapped severance package.
I have documentation of the inaccuracies (one of which could implicate the boss who, by the way, has initiated this severance package.)
I have done nothing wrong in this situation, I've just come across hundreds of dollars and inflated circulation figures that could be pretty damaging to the newspaper. I need to do something pretty quick in order to get this settled.