Facebook – Accidentally unfollowed a friend on Facebook and want to reverse it

I don't think G+ (or any other) will delete your content.

I think there is a best practice somewhere that says "do not delete anything" (at least this is how I learned database design), it's just like in nature "nothing is lost, everithing is recycled". :)

They rely on content—think of Google search—sometimes it seems that it knows what you want to search, beacause the more users search, their database grows bigger and bigger, the more database searches that can compare with the more precise is the result. This is true for social media to, they build a profile for every user, and they build the so called "social graph" of the world (read this interview). :)

What they do with the results... first they are showing custom ads, I think they even sale the results to big companies—they have data that is extremly valuable in marketing. For example: a phone company launches 2 new models, m1 and m2, after a few weeks they go to G+, Facebook, and ask them, what is the phone that users talk more m1 or m2, and what phone from a competitor is on top of users talks?

So you need to know that every time you register to a service like this, ALL your data will be stored forever by the company, be it G+, Facebook... you name it.

That's my opinion.

It sounds like the user has blocked you. In that case you cannot see their posts or comments or their profile and also they cannot see your posts or comments or profile. You will not be able to block them except by email address, but they are already effectively blocked so there is nothing you need to do.

Of course, if they have a friend or family member that can see the post then that person may have shown it to them, or if the post was public then they can see it without even logging in.

In the past it was possible for someone to block you so that you could not see them, and then they could log in when you are not on and unblock you so that they could read your comments, and then block you again when they were done. To stop that, Facebook now requires that you wait 48 hours after clicking on "Unblock" before they are actually "unblocked" and also you can't "Block" the same person for 4 days after clicking on the "Unblock". So if someone is blocking and unblocking you, you will have at least 48 hours to see them (and block them if you wish) before they can block you again.