I finally contacted Laz about this issue (and the "Publishers" category. As we all imagined, he doesn't want to 'sanction' a publishing category as he feels it's encourage authors to avoid sites like SOL (or worse, only post 'teasers' to draw readers away).
Personally, the few of us who do publish are pretty good citizens, in this regard. We use SOL (and any other sites) to augment sales, rather than burning our bridges (such authors don't remain authors for long if they take short cuts).
Most of our sales are 'thanks for the effort' sales, where the readers read the story for free, and then purchase it as personal encouragement. Publishing manages to extend our reach to new readers who don't visits story sites like this. However, I can see his point and hadn't really anticipated my request to be successful.
He (Lazeez) is considering this request (to create a "Lost Authors" category), but he's caught by the same considerations. In short, he's afraid that if he publicly acknowledges authors who've quit reading, loyal readers might quit. Most of us have visited sites for a specific author, and we'll hang around for a long time waiting for new stories, but we'll abandon the site if our favorite author/s quit. So his decision could go either way on this subject.
In general, the yellow tag posted after a year's delay is a reasonable alert, not just for a single story but for the author. If they haven't posted in over a year, chances are they're gone for good. Not necessarily, but the odds are against them. The only issue is, if all their stories are 'completed', you'd have no way of knowing they aren't active. For now, the thread on BTFH is the best reliable source we have.