The Openreach ONT won’t be removed if you change to another provider that doesn’t use Openreach products , which makes sense , you may at some point want to switch back to BT , or want to use another provider that does use the Openreach network , or you could move out and the new occupant wants to use the OR connection, all that would happen is the service would be remotely disabled, physically nothing at your end changes, obviously if you wanted to unplug the ONT and remove the BT router that’s up to you, if you have a relatively new service with BT , you could be asked to return the BT equipment anyway , but not the ONT , that’s OR’s property not yours or BT’s.
If you do use another network provider , the alternative network engineer that installs their service should not touch Openreach property.
