Suppose I post a piece of intellectual property (e.g. an essay or picture) to an Internet forum. The forum has no explicit licensing policy; therefore I assume my work is under copyright.
One year later, the forum updates their policy, stating that all existing posts without explicit licenses attached are considered to be public domain. If you do not assent to this, you may add a license or remove your content. I do neither.
When does my work enter public domain, if indeed it does at all?
My guess is that, after a certain point, my content is now public domain (I've voluntarily, implicitly, ceded my copyright, yes?). However, I would also expect that there would be a legally required grace period for me to remove my content before that happens (if so, how long is it)?