W-2's Filing

If your client bought the LLC, your client is responsible for all tax filings for the year, including W-2s and 1099s. (Although the purchase agreement could have specified some specific things.)

If your client only bought assets, they screwed up by using the LLC's name and EIN.

Just out of curiosity, what did the 941 show for the second quarter?  The old owner and the new owner employee wages combined or did they each file their own 941s for the respective months? 

If your client bought a Business, but not the LLC operating it, this means all of the employees are new hires as of that cutover date. All YTD info for the employees and the employer taxes would start at 0. And this person would need to contact State agencies to become what is called a Successor Employer, to take advantage of any continuation breaks, such as if there is a worker comp rate that is better for the ongoing company that for New Employers, and the SUTA might have a provision for Successor Employer.

It's unfortunate that this is just now coming to light, because there are a lot of provisions that would not carry over to that new entity, just because it hired the same people that were working under the old employer. It's hard to know how many of the provisions were utilized, of course, and who is now responsible for addressing the issues. That can even include benefit plans.

I recommend legal counsel on this, because the old employer/owner should be brought into this discussion, too.