and then the king's whisperer, who has been planning this all along, has one of the mages in his employ dispel it.
The problem I have with all these (otherwise ingenious) schemes is that a mage could do almost the same regardless of whether the salt was made of flesh or not. The spell is instantaneous and cannot be dispelled. You can cast Stone to Flesh on normal salt or formerly-fleshy salt and get the same results as long as there's no salt statue that was a living (or unliving or animated) creature when it got turned to salt.
So making the salt turn to flesh would prove nothing of the origins.
(Regenerate wouldn't matter, since the damage dealt to the creature in salt form wouldn't be converted to non-lethal.)