Migrating disqus comments from non drupal site to drupal 7 site
Disqus offers variety of migration tools depending on your needs - https://help.disqus.com/customer/en/portal/articles/286778-migration-tools. I performed migration of comment threads from static website to Drupal 7 recently. Main change to the pages with comments was new clean URLs, so in my case all I needed to do is to use URL mapper tool. It is very straight forward and comment threads were migrated in minutes.