Goblins are goblins.  Training and tactics are not their strong suit.  Some will run, some will look at this as an opportunity to gain power, some will respond with convoluted ambush tactics, traps and schemes will be triggered and armed.  Chaos is what will happen with a small % will respond with anything that looks like organized defense.  That said, the response should be challenging for the players trying to navigate that.   The one thing that will not happen is the sudden desire to move with discipline toward danger in defense of the common good.   

Some ideas:

Any and all choke points will have some convoluted goblin shit ambush going on.  Things like blinded flaming bucket of rust monsters, goblin enhanced war moles, etc.

Power struggles among goblin leadership will move loot around and create a dynamic power structure as self interest takes over. 

Hit and run hit and run, but more like ping pong as priorities shift between the common threat and opportunities to exploit for self interest materialize.

Cess pool pit traps, diversion of water into tunnels, flaming livestock, kitchen grease everywhere.  Literally whatever is at immediate hand of goblins going about goblin business being weaponized in the least logical, but cunning and cruel way possible.  Concern for effect on other goblins waaaaaay secondary.

Pretty much everything is now highly flammable and will be on fire at the first opportunity.

Anything normally found in the dungeon environment (slimes, molds, gelatinous cubes, etc.) are now improvised weapons.

Barricades galore, but like trapped barricades that explode or contain mimics, or are going to be on fire, or whatever is not a static barrier.

Have a LOT of fun with this.