Destroyed trenches still offer some form of cover, and are often used by infantry. They still require you to climb in and out, preventing you from packing a person away. If the trench is at a angle, there is a good chance you can still move out by going for corners or whatever is the leveled part. If not you can pull people by doing the following

• Grab the downed player and move to a corner.

• Drop the player (This will put them on top of the ledge)

• Climb out of the trench.

• Pick them back up