Has it ever been proven in any of the shows that the transporter didn't kill everyone that used it and just made such prefect copies that no one realized?

Like it created an extra copy of Riker and there was the tragedy of Tuvix. Though I'd say the former is evidence that it is new copies but the latter might be evidence against it, since they each had memories of their time merged when they separated. Actually, that whole incident kinda brings into question what's going on for a transporter to accidentally merge two people and not in a "horrible teleportation into a wall accident" way and then somehow de-merge them.