One point to consider, from the previous thread admittedly, if all the water boils away, what is going to generate the pressure?
Having seen this in the flesh on a 31/2 Atlantic boiler, all that resulted was a lump of hot metal, the residual pressure dropped to nothing very quickly, but of course would have resulted in a flash steam generation should any water have been injected, (This was witnessed at the time when the driver tried to pump water in using the handpump, the resultant 'flash' was coped with by the single safety, blowing off at 80 psi, and dropping back to zero almost immediately).
As it turned out, the driver, who was a novice at the time. was unaware of the very quick drop in water level that can happen on the Atlantic design and the fire was immediately dropped by his supervisor.
End result – boiler was taken off the frames, inspected and retested as per a new build,(allowing for softened copper) which it passed flying colours, and is still in service today.