Is there a reason to delete the branch? I don't think I've ever tried to delete a branch in subversion. I imagine it's possible, and can be reversed if necessary, but goes against my thinking of the repository as a canonical log of all development.
Commits are what's fixed. Branches are basically just mutable pointers to commits.
You can at any time go back to it as long as you know the SHA-1 identifier for the head commit you want. Because of this, there's little reason to keep temporary refs cluttering the ref namespace.
If you really want to keep references to everything, a "git attic" tool exists which allows you to move branch refs out from the main ref namespace into a normally invisible (ie. doesn't show up in git branch etc.) namespace.