It won't help with future data sharing either. I had 2 profiles that I "deleted" in 2011. They won't actually delete the data though, just mark it is as deleted. It's all still there.
Although I read recently they will (or maybe they now do) actually delete that data (but probably only for EU citizens that request it) because of the right to erasure in the GDPR
I don't think it's been confirmed publicly but they maintain shadow profiles. of non-users.
Every single piece of data (e.g. email address, url, picture, device ID, phone location data, event, ... etc etc etc) that any user has that is not directly linked to another existing user is kept in a shadow profile. Of course those profiles will be linked to all the other data that facebook has, including data they've collected outside of facebook itself e.g. every single "social media sharing" button on any website.
For example photos.
All that AI tech they use to identify whether you are in a photo, is also extended to those shadow profiles as well.
Facebook's income comes from selling your data) so all of this freaky, immoral (my opinion) surveillance was originally just to show you an ad for a fucking lawnmower. However everyone has now twigged on to how valuable data is and so it's now spread everywhere - in particular now we hear about the "dark web" think of all the id theft, extortion, blackmail and now election rigging we're getting to hear about.
None of these tech companies like google, facebook etc nor the massive data brokers and advertising industry will ever admit they are culpable though, but they are all involved, it's the business model of the modern internet.
There should be a existential right to privacy enshrined in law. The only way out is through stiff legislation but I doubt there are any brave enough to clamp down on corporations in that way. Corporations now run the world and until their influence is removed from politics I don't think we'll see much progress for laws to protect our data being bought and sold by anyone with enough money.
I know it all sounds a bit too conspiracy theory and David Icke, but I really think that we need protection from the overpowering influence and power corporations have over our lives.
Just like separation of Church and State we need separation of Corporation and State.