I agree with the plan to back out. We're not in a good spot and we really need to get out of there.
Sorry, I think there was a misunderstanding. My plan was for us to stay out of the tunnel and see if dancing lights could reveal any goblin silhouettes in the smoke for archers to take out. Although looking at the situation that probably wouldn't have worked either.
A quick clarification since I'm not sure you are all interpreting things correctly. A group of goblins ran out of the smoke smack dab into you. Hornet and Thaoran killed the first one. But they are essentially engaged with another group of 4-5 (or somethng like that - in the smoke, who knows?). This means you can't just turn and run. Well, actually, you can, but your opponents get an attack of opportunity if you do that. Think about it like this:
1. Hornet and Thaoran could attack first and then run - which allows a free attack by the enemy when they run.
2. Hornet and Thaoran can forgo attacking and use the disengage action instead to get away without provoking an attack of opportunity.
The above only applies to H and T because as the front two they are the only ones engaged in combat.
You can move back 30' - or run 60'. But running takes your "action" for the round and prevents you from either attacking or disengaging - thus you would provoike the attack of opportunity.
All of the above assumes that those behind H and T have cleared out as well to clear the path.
You are currently about 20' or so into the smoky tunnel. From the door to the treeline is another 20 feet or so.
Exactly how all of the above plays out will also depend on initiative rolls - the goblins may get to attack some before you can do anything. (Note that if one of the front goblins goes before you, then they might get to attack twice in the round - their normal attack and then an opportunity attack - depending on the choices you make. Goblins can also chase you and if they run as fast as you do they may be able to move and attack in the same round.)
The fastest anyone could get "poisoned" from the smoke is two rounds - it could happen by the end of the next round if someone fails both con saves. The fastest anyone could collapse from smoke is 4 rounds assuming they fail all 4 con saves. That won't happen if you bugger out now.
Actually Hornet gets "cunning action" as a bonus action which allows dash, hide or disengage. He could use it to run without offering a attack of opportunity. Basically he would disengage as a bonus then move freely as an action.
Hornet will use his thieving ability to perform bonus action of disengage to break contact and then use regular action to retreat. So if he wins initiative he would be able to escape without the goblin getting an attack. If he loses initiative the goblin gets its regular attack and then Hornet moves away instead of attacking. Either way there is no attack of opportunity for the goblin