Hi people of experience!

I'm sort of stuck. So here's the situation, but before that, it's only
for gone-through-already players... since I'm going to mention some details...

Chapter 5 (I think), gone after Irenicus to Underdark.
Rightly okay so far. My party is quite terribly built,
I have to cast elementals and such to nearly all battles in the Underdark to survive.
There's no places left except the Southern Tunnel which has those nasty Beholders.
I even went through that with improved invisibility but didn't find what I wanted.
What I wanted was to find a way to open those gates, to enter the city where I must go.
The dragon gave me already a disguise to fool the guards.
But the problem seems to be that I accidentally killed the guards of the gate before I thought they should maybe left alive.... before I found the dragon.

So there seems to be nothing to do now about it.
There is no way out, so I thought is this a bug in the game...
The gates are closed beyond lockpicking and knock spells.
Would just seem a waste to get this far, and just collapse the save.
Any ideas?

Have you been back to the gates of Ust'Natha since you got your disguise?

If worst came to worst you can fight your way back to the surface through the Kua Toa tunnels.

The chapter exit is in the Sahuagin cave in the west. You can kill and loot the dragon first if you want, it might even be necessary.

No there is only one way in.
But if your party is too weak to fight your way past the drow in KuaToa dungeon, you could just haste your party and run through without fighting, it's not far.

Once your Druid can cast creeping doom you'll do some damage.

The gates to Ust Natha are at the top right of the Underdark caverns. They should open automatically once you have talked to the dragon to get the Drow disguise. (It should not matter if you've killed the one guard outside, I would think).

The war party that teleports in to attack when you cross the narrow bridge is irrelevant. They'll attack always, and you can't get your drow disguise without getting past them. The war party next to the soul sphere will also always attack. Don't worry about those guys either. If you somehow managed to attack the actual Ust Natha gate guards in the far northeast corner, though, and you got the journal update of "I screwed up and the drow have seen through my disguise," then you're not stuck... but you have missed out.

If you truly got discovered, then the drow illusion would be dispelled and you'd be forced to kill Adalon in order to progress. Once she's dead, the exit to the surface through the Kuo-Toa tunnels will open. You'll miss out on some good loot and some good quests from the city itself, but it's nothing really heartbreaking.

hm... okay... I'll go and follow your advice.
The gate I mentioned is the one on top left corner, in the area with the demon altar and the Kuo-Toa pools. So not really top right...
Okay, I'll go venture forth now, thanks everyone :) !

...

Ah found the other gate. Yeah, it was exactly as the dragon said, I got in without problems in the disguise. Just confusion I guess. This really is a great game, shouldn't doubt so much about bugs, haven't seen any way to get stuck so far.

But it was nice to discover the mod-scene at the same time.