I'm not making that claim, and freely admit that I am utterly ignorant about mercurial. I'm merely demonstrating that, contrary to the author's assertion, it's possible to use git without deleting branches and still have a meaningful way to measure whether a branch is "done", and it's the common-sense measure of "has it merged?"
You can change your mind and turn a 'bookmark' into a 'branch' and back again. you can also fold your branch into another one and pretend it never happened. Or you can pick your branch up and place it somewhere else in the tree, or...
To say "I'm done with this branch", merge it to master. This is natural; you already do this.
Now you never need to delete any branches if you don't want to and you can eyeball their status without introducing any misbehaviors or gymnastics.