I can see a use for deleting true zombies. Maybe not a huge benefit, but namespace suck could become a problem.

However, loosing the author name of old nodes, because the user is passed is a no win. There is something to be gained for keeping an author's collected works. This provides continuity of opinion, shows growth of community members, and gives us cultural continuity. We are a community, and records of the past are important to the community. Besides, old nodes may point to an old user . . .so the link remains pointing to dead nodes? No, that won't do. Besides, it'd be a hassle to write such a tool, with dubious benefit.