I think there is a difference between "reactive: we're sitting in our warcamp waiting to be attacked" and "reactive: we're out in the world encountering difficult situations and having to decide how to deal with them." Especially since there is definitely a style of dungeon mastering that's just throwing plots at your players and seeing what happens. In fact, unless you're running a true sandbox with a quest hook in every direction that your players must decide between, having your quest giver offering a single quest for a given game session isn't too much further down the spectrum from purely reactionary.

As for what the Goblins will do next... well that's anybody's guess at this point of course. Presumably they continue with the plan of returning to the main camp, only now with a lot more experience dealing with adventurers and crazy problems. I doubt things will be that easy, of course.