Is there a reason to end this mission?

Solution 1:

Nope, feel free to farm to your hearts content.

Solution 2:

You can farm on the map as long as you want until whenever you want to retreat. I used this opportunity to:

  • Promote all of my squad members
  • Farm resources, corpses, and also equipment drops (like weapon mods)
    • Great so you can sell them later on in the Black Market for extra supplies