Basically the game is programmed so that you absolutely cannot proceed without Shadowheart's artifact...you cannot get out of that. No matter what, that artifact is either with her in your party or you are forced to kill her for it.
If you push her someplace you cant get her corpse or leave the artifact what happends i wonder
When she dies there is a cinematic that shows the artifact flying straight at the main character as a metal to a magnet and then the player character tries to toss it only for the same thing to happen again and again. But if you were to somehow succeed to get rid of the artifact you'd only break the game's story and progression. So don't try that in the full game...unless you really want to start a new save over from the beginning.
