I have had many friends rage quit .. life.
So the idea of rage quitting an online forum, is inconsequential compared to that.
I literally went threw this quite recently as you know.
I know a few high end forums that have daily rage quits from 10-20 year vets. Dying forums.
Politics is what is killing those forums. but anything can lead to it.
This is why I say it is risk mgmt.
But if managing it becomes successful?
When I said "**** it" to Manga Raiders after a 13 yo was allowed to retcon (the biggest crime against writing) a communal piece, I didn't delete all my stuff. I left it so some could learn from it (they didn't). I'm not like most people though.
I think I know who you are talking about. But I deleted my stories. I think I left my advice, but these stories are better off elsewhere.
Knowledge is critical. maintaining a record of what happened is part of that. Letting people delete parts of that record is unforgivable.
In terms of a forum, unfortunately the info can be expendable. Not a lot of people look for records unless something crazy bad went down. And usually by then if people are aware they screenshot it.
But at that point it's not the forum controlling what is recorded. Someone just taking advantage of a feature outside the forum is. Again, YouTube, Facebook, Deviant Art allow it.
Like I said, someone did something to deserve the rage quit and content lost. At that point, we have to be held accountable. It's not pretty, but it's not wrong either.