You’ll mostly be coming across AI until you have to get to the exfil zone. Players will usually have the option of 1 or 2 exfil locations so once everyone has looted/finished contracts/killed AI they will go to the exfil location and call in a helicopter. That exfil helicopter can be hijacked by folk who are waiting in the exfil area, so it can be a tense, mad rush getting to the helicopter. You aren’t safe when you first board it either, you can be shot out of it if you poke your head out too much. All the weapons you find/loot in DMZ are instantly unlocked and can be used again in warzone/DMZ. Don’t know if they can be used in main multiplayer, I’ve been told they have been haven’t checked.