I always thought 'trending' was about clicks not about posts, so as long as people are still clicking it will stay. A thread with 'famous person' in the title would be v popular with people wanting to know who.
<whispers> I don't loathe the word trending , though I know lots of people do. Must admit I thought it was changed from Most active just in a (misguided?) effort to appear, erm, trendy. But now I see Trending actually means something different, and can include not just slow-moving threads but deleted threads too, that just seems bonkers.