If you want to use the inventory, you'll be safe to do so-you become invulnerable when it's open. Players won't be able to use VATS while using the multiplayer mod, as it's been disabled. If the host leaves the region, then a new host is chosen, and the NPCs will resynchronize to them. That means that if a player connects to a host that has killed an important quest-centric NPC, then any relevant quest could fail. Reddit user and modder Nvmp_corporal explains how it works, saying all NPCs in a certain region will be synchronized to a host, but quests won't.
New Vegas: Multiplayer will allow you to get thrown out of post-apocalypse casinos with your friends-or attacked and killed by Deathclaws, if that's more your speed (via PC Gamer).
