The root canal won’t affect the tooth/jaw relationship.

A root canal takes out the nerve via the hole that it sits in in the center of the tooth and running down the center of the roots. It is then replaced with an anti-bacterial rubber substance and closed up with a filling and most of the time a crown/cap as well.

Outside of the root there are those little periodontal ligaments that attach the tooth to the bone, and those are still alive after a root canal. Think of them as strings and when we get braces/chew/put force on the strings it tightens them on one side of the tooth and loosens them on the other. Where the right strings are, the body knows to lay down more bone because the current bone needs to be stronger to stand up to all the force, but where the loose strings are the body knows to get rid of some bones because it’s being essentially useless in this area where it’s not taking much of any forces. The body is doing its best to adapt to the pushes and pulls that is put on it. This is true of all bones- if you work out a certain muscle the corresponding bone will get stronger/denser in the places it interacts with that muscle.

What you’re describing sounds more like someone trying to prevent wear with a retainer as a guard more than actually used as a retainer. Not abuse and can be really important to protecting your teeth. Wear is more than just cosmetic when it’s a chronic thing that happens for a long time

Bone is constantly being broken down and remade so that it can adapt to the forces we put on it with our muscles and it doesn’t get too brittle

Dentist here. Depends on how your teeth were before you got your braces. If they had massive spacing and rotation, then they will likely slowly go back to what they were. It’s so variable person to person that we always say wear your retainer nightly for life