Even with no publishing activity to that blog for the next century, and barring any mistakes in ownership, your blog is yours, forever. We also know that when a blog is deleted, the URL that it's published to is locked to that blog, for eternity, to prevent a hijack of the URL by spam blog publishers.
So what if you have a URL, and you want to make it available to someone else?
If there's a specific person that you want to have the URL, you turn the blog into a stub, then you transfer the blog. If you want to make the blog available to the blogosphere in general, you simply recycle the name and make it available to the public.
- Edit each post, and replace contents of each with the caption "Post Deleted".
- Republish the blog.
- A month after completing Step #2, delete all posts. Publish one post, "Blog Deleted".
- Six months after completing Step #3, republish the blog under a 16 to 24 character garbage name, making this name available for some lucky blogger.
- Make up a blog name that is unlikely to be in use now, or ever in the future. In this example, I'll use "zmxncbvalskdjfhgqpwoeiru".
- Go to Settings - Publishing, and re publish the blog as "zmxncbvalskdjfhgqpwoeiru.blogspot.com".
- Your having re published the blog as "zmxncbvalskdjfhgqpwoeiru.blogspot.com", the current name (presumably, of some value) is now available to the Blogosphere, in general. You are done with this exercise. The inhabitants of the Blogosphere thank you (should thank you) for your altruistic attitude.
- Then, delete the made up name, such as "zmxncbvalskdjfhgqpwoeiru". That blog will stay on your dashboard for 90 days, to give you a chance to change your mind.
If you want to make the URL available for re issue to the public in general, you have only to re publish your blog to another URL. If you intentionally re publish your blog to a different URL, the first URL becomes available to the public.
If you have a popular URL allocated to your blog, you tire of the notoriety attached to the URL, and you wish to let others take the responsibility, just re publish your blog to a new URL. And the responsibility is removed from your shoulders.