If you separate or get divorced and then change your mind and decide to get back together again, generally the law takes the view that that is entirely your business and nothing to do with the law at all.
However, unless it explicitly says so no order of the court is changed by the fact that you get back together again. In particular once you have got a decree absolute you remain divorced irrespective.
So if you do get back together again you need to ensure that any court orders that you don't want anymore are revoked, and in particular if you want to get married again you have to go back down the aisle.
If there have been domestic violence proceedings and you change your mind, then it is especially important that you go through the proper legal procedures to revoke any court orders that might have been made because otherwise one of the couple might be committing a serious criminal offence of breaching a court order by resuming a relationship with the other.