As with building any website, there is obviously a lot of thought and research that needs to happen before you shut down one website and move content and information to the other. Obviously your main goal is to properly rebrand one, or both of your companies. With that, rebranding your website is also a high priority. The more complex the merger of your companies, the more complex the merger of your websites will be.

Which Brand Will Be The One Moving Forward?
Will it be brand A, brand B, or brand C, a completely new company created by the merger, or even a hybrid of your brands? Once you have this figured out you can begin moving forward with your website.

You’ll want to ask yourself the same questions you would if you were building a site from scratch. What is the purpose of the site? What will drive visitors to the site? What do we want them to find on the site? What do we want them to do on the site? Is there an overall goal for the site?

Now, what information and assets can you use from each site? Is there content, images, video, blogs that you can transfer easily and effectively to the new site?

What about SEO?
That is a big concern anytime you “shut down” an old website and launch a new one. You want to make sure to set-up 301 redirects to your new site from your old one. Create a Sitemap of your old site and one for the new site and make sure that each page on the old site maps to one on the new site. I would avoid simply mapping the old site to the home page as that won’t be as valuable to users and search engines as manually mapping each page. It is a tedious process but will certainly pay off.

You can find links to your old site and email the webmasters asking them update those links. This is usually a long process can have mixed results. It is probably best to work on the existing links that provide the highest level (and quality) traffic, and then focus on building new links, I wouldn’t suggest trying to get every single link out there updated.

Branding
Make sure any old ads that you had running, whether through AdWords, Bing, or other online or offline media point to your new site.

You should probably also make sure that the new site acknowledges that the old site doesn’t exist anymore for a few weeks or months depending upon the size and complexity of the merger. For instance something like “Brand A is now a part of Brand B” or “Brand A and Brand B merged to form Brand C which will bring you all of the values of both brands under one roof”

Finally

There is obviously a lot of information to uncover and digest before moving forward with the merger. Make sure that the website properly presents your new brand image and message while also doing your homework to try and save as much of the SEO value of both sites before merging them.