Seriously, getting yourself in a situation where you may be blackisted (e.g., in case of a police raid or some other way they will learn about the legal status of your friend) is NOT an option.

My concrete, practical advice would be:

Finish your employment period as agreed upon with your "employer", get your cash, and leave the country. From outside, then try to find a new, legal job with a real employer who get you the necessary papers to apply for a working visa.

Any other advice contrary to that would not be of benefit to your friend - so, for example, if you decided to leave your current job, where would you go, eventually becoming homeless and have no money at all? Not very nice if you have no sufficient resources of your own.

Thus, please, your friend may reflect before before he or she is doing anything in one way or the other!

Good luck!