Seriously, it's an interesting exercise of thought. Things are saved 'forever' once posted online, simply due to the probability of an individual/system making a copy being high enough vs. the number of viewers. But then, although all this information is archived, the vast amount of data it sinks with renders it just as anonymous as something that wouldn't have been posted in the first place.
In some perspective, information posted online is there 'forever', where 'forever' means 'until it gets effectively submerged in a sea of similarly meaningless documents, lost in a maze of 404s'.