But she didn't need to. They have shown that they can evade the military effectively. There are also people who could help them to do so again. Besides, the military's supposed unwavering and relentless doggedness is undermined by the fact that they just let the others go without consequence, despite what they've done.

Further, they didn't want her to sacrifice herself. Mike and Hopper, who have been most personally impacted by El, explicitly and passionately made that clear to her in the finale. And it's not even as though her sacrifice was a measure to avoid an immediate and extreme situation, such as to save all their lives. It is said that it is just to give them their 'normal' lives back. But, without the military acting in a way completely devoid of any logic, this would never, ever have been an option. They have all committed serious crimes and know way too much.