It seems the "MILE" resets when I leave and have not cleared it of baddies. I killed 4-5 but realized I was over matched. I left and they all seemed to respawn. Is this correct?

What if I do clear it and leave? Does it reset again?

I just did not have enough supplies/firepower so need to go back after some prep work.

Had no idea it was going to be that effing hard.