The news of a possible complete combat guide adds a huge amount of excitement for the trip. Wavering through the scorching desert was originally just a means to an end, but now it's a treasure hunt.
They will have the Primordial Shamans serve as their transport, as they're well beyond human sized, while the Greater Lamia Scourge Casters can search for portals into the lost empire. The shopkeeper says nothing horrible happened that ended them, the sands just slowly took over everything and people left, leaving behind entire cities full of anything they couldn't carry. In the end, one of their last great Sorcerers cast a barrier to protect what was left and then passed away, leaving the ruins to be buried by the sands.
It sounds a bit fantastical, but what tale from thousands of years ago doesn't? The stories get altered with time to stay interesting, or they get forgotten.
