The way it has worked in the past is so long as you acknowledge they are leaving then its been okay.
So if the person is hounding them, they say in their closing X is 2 for example and someone comes after them on that and just goes to town on it then that does get snapped at,
Especially if it involves cussing or generally being a jerk.
To be clear I have seen the other side as well.
And it does come across as getting the last word if the leaving person is using insults for example I once had a poster call me the resident forum troll 2.0 then block me. Which just made it clear they were trying to get the last word as all it did is block them from seeing my posts but not the forum at large and that poster was shall we say bitter about the whole thing to the point MODS came down on him.
Basically it tends to boil down to dont be a jerk leaving and dont be a jerk acknowledging someone leaving.
Now its late over here and I need my sleep so good night