When do you think the ptsd in soldiers ends without therapy?

2-5 years. Combat-related ptsd often subsides on its own in 2-5 years, though in some cases symptoms can persist much longer. Drug and alcohol use, unemployment, and poor social support worsen diagnosis. Conversely, a strong social support (including a healthy marriage), gainful employment, and a healthy lifestyle all improve outcomes. Of course, those that receive treatment improve much faster.
Never. Plato wrote "Only the dead have truly seen the end of war." By this he meant there is no cure for PTSD in combat veterans, only management. I tell the vets I work with that we are all students of PTSD, as it comes in many varieties and usually is not curable.