That is a very weirdly specific scenario that won't ever happen, so why bother asking about it? Humans will always find new things to be valuable. There will never be a time when there is no work left except for producing heroin. People will always want what something no one else has, or something that someone else has that they do not. Humans will strive to create new things, thus creating value. I can see you are trying to pigeon-hole the conversation in a social media vs. heroin comparison, but that just isn't a good representation of the issue.