I think it depends on the intent of the thread. If someone is upset or hurt, and are posting to make their point known, so be it, but don't belabour the point.
LB and Francois are examples of this. Made their point, said goodbye and stuck to it. Though I admit I miss them both. Enjoyed LB's stories and pics of his success with his basketball team. And Frank's sardonic wit, always kept me in stitches.
However I've seen quite a few, say goodbye, ask or get themselves deleted, than ask to be reactivated, only to start stirring up the pot again. I don't think the mods and administrators need that aggravation, especially if it is repetitive.
And then there are those who simply disappear, without a trace as Avishai mentioned about OUTLAW. I think it would be only a common courtesy, if a regular poster is going to be absent for a while to let us know, so we don't worry. I know I get concerned, if someone suddenly disappears, without a word.