I am not an expert, but don't think we should scare ourselves. If the employer requires you stay there permantly, ask for a contract, or a raise. As long as I resign your job professionally, I don't see any trouble.
Why does my employer want to pay hundreds of dollar per hour for the corporate lawyer to suit me? The law in this country is tricky. One may contradict another, for example, the immigratin law may contradict the employment one(I don't know for fact). If my employer goes nasty on me or uses this case to threaten others, hehe, maybe my chance to get a couple of million and retire earlier.