An idea I had the other day is a "resurrect" feature. If you have X karma and showdead turned on, you have an upvote link for comments made by hellbanned users (unless a moderator killed that comment specifically). Two upvotes by non-hellbanned users leads to the comment being resurrected, so those without showdead can see it. If a user consistently gets their comments resurrected, they may be eligible to have their entire account resurrected.