I don't think WWE will be able to shut TNA down unless WWE was able to pick up main event wrestlers that keep TNA from being another boring wrestling promotion, but seeing as how I don't ever see Styles, Angle, Joe, etc joining the WWE TNA has a better chance than WCW did to overtake WWE one day and be the more dominant wrestling promotion.
But the problem is WWE didn't really take any of WCW's main eventers, they took younger guys who weren't getting pushed like Eddie, Benoit, Jericho and gave them a push and made new stars. If TNA continues on it's track about not pushing new guys WWE could just repeat history.