I am in the same boat. Your lawyer is probably right. There are few opinions about company mergers and aquisitions. Check on murhty.com for some view. But in summary,
1- One opinion says, the new company may be considered a "successor in interest" which meas that they automatically sponsor and assume responsibility for the immigration petitions filed by the old company. However, this depends on how the merger was executed. So your company lawyer should be able to advice on this.
2- Another opinion says an I-140 "amendment" is needed (again depending on the nature of the merger). The amendment is only to show the name change of the company based on the merger. It is simple, but as every thing with the US CIS, it may take about three months.
In my case, my lawyer is going by the "successor in interest" argument.
I hope I had helped !!