If the players talk their way out, they have a lesson in considering their actions and thinking things thru more thoroughly. If they have to escape, they could risk rewards being posted for them. No good deed goes unpunished indeed
Whats the actual goal of the GM here? Of the players? Are both satisfied?
the GM has basically turned the the PCs from heroes to zeroes. By virtue of DM fiat.
the players may have just wanted to do some good in a world where they can, and the DM not only thwarted it, is discouraging it.
Even in Reynard's post, about "don't be heroes, be treasure hunters". If the DM decides to make negative consequences for the players bringing in all this gold, he's discouraging players from what they wanted to do:
go treasure hunting
stop the bad guys
There's a fine line of course. The GM can't be making things too easy, ignoring obvious consequences, etc. But he does get to choose whether to make things worse for the PCs on a whim.
Deciding to make things significantly worse when the player successfuully executed their game goal is thwarting. And thwarting is generally a bad GM behavior. It's basically saying, "don't do that!" to the players.
So, while it may be realistic to determine that bringing in numerous refugees, mass amounts of gold will impact a society in a potentially devastating way, it's not very fun. And quite possibly not the kind of game your players want to play.