Help!! Am I staying illegally with E-2?

My friend asked me questions with her E-2 visa? Please answer to the following question.

My friend\'s family came to US with E-2 visa around 3 years ago. Around one year ago, husband returned back to his country. However, dependents (wife and son) did not leave the US and have been staying in the US. Dependents have DOS date (#/##/2003) in their I-94. After leaving the US, husband visited once US with B1 visa and went back again to his country.

My question is whether dependents are staying in the US legally or illegally? Because I was told that if the principal visa holder is leave the US and doesn\'t maintain the original visa status, dependents\' visa status is canceled automatically regardless of their DOS date of I-94. Please clarify this question!!!

Thank you in advance for your input regarding this question.