When you are in a friends lobby and they leave the game (ie. ALT+F4 or Quit), then it puts you back into your own instance.

it puts you back into a raid/dungeon on the same mission and not back at the camp.

however, when using the map/overlay it still lets you select a new mission even though you are not in the camp.

The objectives still work but do not have any highlights or waypoints and the mission map does not work.

you are able to complete the mission still and then it puts you back into the camp as normal.