Your blog depends upon traffic for its success. Anything that affects the traffic to your blog, such as a change in the URL, affects the success of your blog. If you republish your blog to a different BlogSpot URL, as with migration to a custom domain , you will not lose any content. Both comments, posts, the template, and all custom settings, will stay with the blog. And if you plan the republishing effort, you can minimise the loss of traffic.