Playing

Coming and going

What happens when somebody leaves, when everybody leaves, and when you all come back.

There is no host, so nobody’s departure is the one that ends the session. Every person in a Fragment runs their own copy of the world and simulates the part they are standing in. This page is what that means on an evening when people drift in and out.

Regions held by the people currently in a world. Schematic, not world data.

When one person leaves

Your friendThey quit the normal wayabout 2 seconds
The game says goodbye before it closes. What they were simulating passes to somebody else, and anything mid-air carries on, because the ground it is above never stopped being simulated by a person.
UsOr their machine dies without warningabout 30 seconds
Nothing announces a power cut. The others wait out the same pause vanilla gives a player whose connection hiccups, then pick up what that person was holding.
YouEither way, nobody does anything
There is no host to restart, no world to reopen and no save to transfer. The chat line saying they left is the whole of the event.

When everybody leaves

The world stops. Nothing is running, nothing is ticking and nothing is being charged for, because no machine anywhere exists to hold it. Every chunk anybody changed is mirrored off-site as an ordinary Minecraft save, and the next person back pulls it down and starts simulating where they stand.

Coming back to a world

It is in your server list: A Fragment you have joined stays in Multiplayer under the gold divider. Joining it again is one click, and nothing has to be coordinated with anyone.
Nobody else has to be there: A world with one person in it works exactly like a single-player world that other people can walk into later.
Your copy catches up: Anything that happened while you were away is applied to your copy when you arrive, and the game prints a line saying what changed.
Nothing expires: A world that nobody visits for a month is still there. Only deleting it removes it, and even that leaves it recoverable for a day.

What a world does not do yet

Stay up with nobody in it. Always-on worlds are planned and not built. If you need a world strangers can wander into at four in the morning, this is not the shape for it, and renting a box is the honest answer.
Run the Nether and the End across the group. Sharing is the Overworld for now.
Promise durability. Saves are mirrored, and we are not yet in a position to promise they survive everything. Back up anything you would be upset to lose.

If your own connection is the problem

Two things happen automatically, both of them the mod keeping the evening playable for everybody else.

Authority is handed away: If your connection is saturated while you are simulating, that work moves to a peer and you are told it happened. Nothing about your world is lost; you are simply carrying less of it for a while.
One of a pair is disconnected: If two people are online and genuinely cannot reach each other, one of them has to leave, because a world half of the group cannot see is worse than a world one person has to rejoin. The disconnect screen says so plainly and invites you back.

The measured figures behind all of this — how long a handover takes, how long a crash takes to notice — are on how it works, with the method beside them.