You will pay regular income taxes and a 10% penalty on the amount OVER what you contributed.
For example, if you contributed $10,000 to your Roth 401k and it is now worth $15,000, you will pay regular income taxes (often 25%, plus State, but it depends on your income) and the 10% penalty on the 'extra' $5000.
As a side note, you say "if I decided to keep the money". If you missed the 60 day window, it can not be rolled over. However, because you did not yet cash the check, it *MIGHT* not be considered closed or withdrawn yet (you would need to contact the administrators of the 401k to determine that).
