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When I worked on the rebrand from SEOmoz.org to Moz.com, we faced exactly this situation. You can watch my Mozinar about it here https://moz.com/webinars/domain-migrations-lessons-from-the-moz-transition. In brief: You should expect to see a temporary dip in traffic and rankings, but it's totally reversible. Do as much link reclamation (reaching out to sites that link to you and asking them to update their links) as you can. Plan for a concerted link building effort to the new site to coincide with launch. Go page-to-page with redirects wherever possible. Use the Change Address function in Search Console. Make sure that pages that rank for core terms now redirect to pages that target those same terms. I've also noticed that Google has been slower than usual at indexing new pages lately, sometimes taking upwards of a week, so keep that in mind as you check for your new site being indexed. Good luck!