We have a client who carries 4 product lines from different manufacturers under a singular domain name (www.companyname.com), and last fall, one of their manufacturers indicated that they needed to move to separate out one of those product lines from the rest, so we redesigned and relaunched as two separate sites - www.companyname.com and www.companynameseparateproduct.com (a newly-purchased domain). Since that time, their manufacturer has reneged their requirement to separate the product lines, but the client has been running both sites separately since they launched at the beginning of December 2016. Since that time, they have cannibalized their content strategy (effective February 2017) and hacked apart their PPC budget from both sites (effective April 2017), and are upset that their organic and paid traffic has correspondingly dropped from the original domain, and that the new domain hasn't continued to grow at the rate they would like it to (we did warn them, and they made the decision to move forward with the changes anyway). This past week, they decided to hire an in-house marketing manager, who is insisting that we move the newer domain (www.companynameseparateproduct.com) to become a subdomain on their original site (separateproduct.companyname.com). Our team has argued that making this change back 6 months into the life of the new site will hurt their SEO (especially if we have to 301 redirect all of the old content back again, without any new content regularly being added), which was corroborated with this article. We'd also have to kill the separate AdWords account and quality score associated with the ads in that account to move them back. We're currently looking for any extra insight or literature that we might be able to find that helps explain this to the client better - even if it is a little technical. (We're also open to finding out if this method of thinking is incorrect if things have changed!)