Usually are deletes not true deletes they are just set as deleted, often with a date or a boolean/bit in the database. I have never been to a company where true delete is the default. They are usually manually or scheduled. Just like non IT companies like banks store your info for many years. Even after you are not a customer because of the law.

So it is better to over write it. Often is that only backed up. Some have systems where nothing is truly overwritten because they need to see all changes like version handled web pages like Wikipedia but I would say most overwrite. It can be more complex than what is worth (to keep all the history).