The way it works currently is that quests are clientside, they still take place in the world but one player in a location will synchronise entities/NPCs to other players around them. The developers went on Reddit to discuss this: Killing or pick-pocketing an NPC will have lasting effects for story progression - you can fail a quest you never started. The decisions of one player can affect everyone. The developers are working to give all players an equal amount of influence. This won’t just be Fallout: New Vegas with friends For now, the feature just doesn’t match with a multiplayer game. Finding a way to install VATS in the game’s final version is being discussed.

More concerning is the use of VATS being completely shut off - no more slow-motion high damage attacks. Closing the menu should resume normal function. Rather than the game pausing every few seconds while you check stats or change weapons, players accessing Pip-Boy menus will become impervious to all damage. Using the Pip-Boy will no longer pause the entire game world. A few of Fallout's key features have been removed/downgraded. This ambitious mod has several key differences from the original game.

Fallout new vegas multiplayer