I had a friend, and I had a blog. I gave my friend control of my blog - and now, I have neither a friend, or a blog.
If you have a blog, and it's yours alone, then it's yours - for eternity, or until you give up control. When you make your friend a blog administrator, you give up control of the blog.
If you give a friend control of your blog, and he (she) decides to remove you from being an administrator, the blog becomes her (his) property.
You give someone else control, and you have lost control.
Once you give up control, and somebody takes control of your blog, it ceases being your blog. Blogger can legally do nothing to assist you, your only recourse is with your (former) friend.
Disputes over blog ownership
Blogger is unable to mediate disputes over ownership.
A blog ownership transfer is final - regardless of the motivation behind the transfer.
A custom domain published blog has intriguing possibilities.
If the blog is published to a custom domain URL, the published domain URL is now under your friends control, in Blogger. You can change or delete the domain address, using the registrars zone editor - and that will stop the blog from working.
Changing the domain setup won't get you either the blog, the BlogSpot URL, or the domain URL - so you can re use either, in Blogger.
As soon as you setup a new blog, and try to publish the new blog to the domain, you'll see another (not!) old friend
Another blog is already hosted at this addressor
Key already exists for domain ...Without publishing the Blogger blog back to BlogSpot, before you kill the domain, you will break the Blogger / Google database entry for the domain. And only your (former) friend can publish back to BlogSpot.
You lose both your blog, and your friend.
You can stop the blog from working - but it will be a pyrrhic victory. Neither of you will be able to re use the domain URL - and you will have neither a blog or a friend.