Romeo and Juliet die because of WILL. In the story there is evidence that they die because of will. Tybalt wants to fight with Mercutio, but Mercutio knows that Romeo will die if they fight. So Mercutio fights with Tybalt to save Romeo. To marry with Romeo Juliet drinks drug and pretends to be dead. After Romeo sees this, he drinks poison and Juliet wakes up, see Romeo dead and stab herself with a knife.