DB Partial Term or not?

I need help regarding DB partial plan termination. Below is the situation.

Company A sold company B. All company B unvested employees who had accrued benefits. Do the employees get 100% vested?

2011 -Form 5500 showed 178 active participants.

2012 showed 0 active participants. 

Does this consider Partial plan termination? I thought it was, but my other co-worker told me it was not. I like to find out if is there any exemption that the plan was not considered partial plan termination. Am I missing something? 

Thanks in advance!

If all of the active employees terminated as a result of the sale, it is obviously a partial plan termination and every impacted participant would be 100% vested. 

concur with Effen.  Hopefully the amendment and 204(h) notices were handled properly and timely.

I don't think a 204(h) notice would be required.  They all terminated employment, so no plan change to report.

true, my bad - feeling the impact of approaching 9/15 i guess....

Thank you so much for all the responses.