So, again, if theplotplot point / element of conflict in the larger plot was "save the town of Highrock from the orcs of Thung", and, instead of (collecting the seven super special secret McGuffins and) fighting the orcs as the plot calls for, the party saved the town, by starting a week-long forest fire between the town and Thung, and evacuating to Gondor in the interim, why do you consider this a pebble?
Understand, I ask in small part because you claim to be a huge fan of railroading. I can see many possible horrible answers - many of them involving railroading - and many possible good answers to the question. Let alone the many answers that i wouldn't consider merely ripples, that perhaps we are calibrated to describe differently.
So, would you consider this course of action jumping the rails? Ripples? Disruptive players? But, most of all, why? What happens to the rest of the plot if Thung isn't dead, and, in fact, now occupies the village? Where do you go from there with the plot once one element of conflict is resolved in an unconventional fashion?