Comment by motorest

> If you try to redact a part of the past, it can also affect the present, as any time traveler knows.

That's not how snapshots work. You record the state of your system at a point in time, and then you keep all events that occurred after that point. This means you retain the ability to rebuild the current state from that snapshot by replaying all events. I.e., event sourcing's happy flow.

> User B was able to send a message to user C, and thus start a long thread, because user A had introduced them. With user A removed, the message replay chokes at the attempt of B to communicate with C.

Not really. That's just your best attempt at reasoning how the system could work. In the meantime, depending on whether you have a hard requirement on retaining messages from removed users you can either keep them assigned to a deleted user or replace them by deleted messages. This is not a problem caused by event sourcing; it's a problem caused by failing to design a system that meets it's requirements.