University of Utah - Go Utes!
You start where you were when the gong went off. A common strategy is to ignore the gong and keep eliminating crystals and exploring.
I think you meant to say that you start wherever you were when the doors shut, not where you were when the gong went off (unless you do not move during the time between the gong and the doors shutting). Example: gong goes off (Oh no! Get back to the start chamber, quick!), you frantically head back, but the dice are not kind to you and the doors shut when you are still two rooms away. At that point, you dicard one die and then start exploring again from the chamber you are now in; the chamber that is two rooms away from the start chamber; the room where you were when you heard that soul-crushing sound of those doors shutting!
And, I'm going to agree with the other post that losing a die makes things very difficult. I generally try to hang onto them at all costs.