It’s silly how “the internet remembers” saying gets repeated. That was true pre-2010 roughly. These days it’s evidently not that difficult for someone to be disappeared or disappear themselves from the internet.

Sayings like this are about threat modelling (worst-case scenarios). If you post something to the internet you need to assume that it will be preserved for eternity. If you want to preserve something on the internet, you need to assume that it will disappear.