Cam Banks said:
Dragonlance is a lot more than draconians.
And the same goes for other worlds and monsters, which I guess was Merric's point.
I think we should once more think about why this theoretical recreation of the rust monster has a gradual weakening effect that evaporates, rather than a puff-steel-gone effect.
Is it to somehow coddle players? That's really unlikely - the DM is the only person who can really coddle players. Everyone, including themselves, can make it hard on the players, but only the DM is the one with the power to coddle.
Why is the effect now gradual? It gives a warning. Much like statues in a medusa's lair. Much like the stories about the local forest, with a deadly fey, or the local sea with its horrid hag.
Why does the effect evaporate? To ease the flow for the DM, if he wants that. He could state the next encounter after the effect evaporated, or directly after the last rust monster is killed. It is notable that the same thing would apply if the effect was permanent, but repairable. Give the players the knowledge that they can do something about the status of their equipment, and they may be willing to continue on with their sub-par equipment for a bit until they can rest and repair.
Is that different from the scenario that they "could just find and rough up a few kobolds" that has been proposed for destroyed equipment with the old rust monster? Yes, and extremely so. For that scenario to work, the DM must coddle the players. Maybe even going so far as to include those kobolds/goblins/convenently forgotten armory that the rust monster ignored for some reason. Realistically, the players should also be worried that they might encounter something they would need their equipment for. Perhaps they encounter a few giants, rather than kobolds? A stalking assassin? The characters can't really know, can they?