A: Deleting the blog will not make the URL available for anyone (including you). You need to transfer ownership properly.
Make the blog in question into a team blog, with two members, then removing the original team member: http://www.google.com/support/
Another way is to vacate the blog address (URL):
1. Sign on with account A (using your friend's ID and p/w) to his dashboard
2. go to settings>>publishing>>Blog*
4. do the word verification.
5. save settings
6. sign on with account B (preferably on another computer): www.blogger.com
7. create a blog
8. choose the name you want as your URL
9. continue to make a post on your blog.
10. publish post
( later on, when you are free, return to delete the blog (xyz123) from your friend's dashboard.)