Micro-blogging website Tumblr allows you to create as many blogs as you like under your account, and you can delete any of your secondary blogs without affecting your primary blog -- the one you create when you sign up; however, if you delete your entire account, every blog, post and piece of data associated with that account is permanently deleted and can't be retrieved.
Although you can't reactivate a deleted account with all content intact, you can rejoin Tumblr using the same email address you used previously for the deleted account and recreate the URL from your deleted blog if no one else has taken it since you deleted your account. Your blog posts and images from the deleted account are still gone, however.
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Instead of deleting your entire account you can place a password on a blog you aren't using now but may repurpose in the future, which allows you to keep the URL but prevents other Tumblr users from seeing or interacting with the blog associated with it. You can set a password under the Settings menu -- this will only work on secondary blogs, not the primary blog; the primary blog always remains public.