My group didn't fare quite as well...
Their approach to the chasm worked a little differently to begin with - I didn't like the very linear path to Sith Morcane, or the fact that the outpost was so close to the crypts, so I added a small network of caves between the two places. One of them also happened to contain a secondary passage to the chasm (which could only be found through very careful exploration or luck - my players found it because one of them ended up falling around 100' and almost hitting the opening...), allowing them to bypass the outpost.
In any case, they arrived at the chasm through the "back" passage, noticed the Fang of Lolth's hide-out on the opposite side of the chasm, used Stoneshape to make a bridge leading to it, and encountered and ran off the Fang.
They were kind of stumped as to what to do afterwards - they noticed the peripheral strands of the web, and deduced correctly it was the lair of something large and unpleasant - unfortunately, they weren't expecting the "city" of Sith Morcane (they actually managed to interrogate a Drow in the crypt level, and got some information, but not all of it) to be so close to the surface... So they decided to see if they could draw out whatever was lurking in the web and nuke it.
Which led to the firing of flaming crossbow bolts into the web, followed by a fireball at the first sign of movement, a rather determined response from the Sith Morcane spellguards, and the party's disordered retreat back to one of the outdoor crypts outside the complex.
Since they alerted the city, and didn't hide well, that same night the drow "armed response team" came after them, and attacked before they could recover spells... The party sealed the crypt with Wall of Force and decided to use Invisibility Sphere and Fly to make a run for it - not a bad plan.
Unfortunately, they previosuly destroyed the door breaking into the place, so their preparations were fairly obvious to an Invisible drow Arcane Guard posted right on the other side of the Wall of Force as a lookout by the drow priestess while the Quth-Maren started to pound on the walls using acid and brute force to begin making an opening and put pressure on the party. Which meant that, since they took a while preparing, the drow priestess cast Invis. Purge, the fighter-mage used See Invis., and the moment they were out the door they got hit with two Dispel Magics, on which I rolled obscenely well, leaving most of them walking and visible.
They reacted rather badly to that - if they stood and fought, things would have been hard but still winnable, but several people routed, and the two that decided to stand and fight (I'm not sure whether it was foolhardy bravery or the fact they were the only people in the group with a move of 20

) got Flame-Striked twice and burned to ash.
The rest of them dragged themselves back to town, rested a bit, recruited replacements (since no True Resurrection was available), and went back.
They found the "back door" blocked with rock, but they bypassed it with Rock to Mud, and entered the chasm... This time, they were stealthy about it, but they didn't use any divination or scrying, and ended up getting screwed over by a couple of very simple Alarm spells the drow put up now that they knew for a fact there were intruders skuliking about...
Imagine - the party strung out along around 100-150 feet of the cliff-face, flying and spider-climbing, when the advance scouts (Druid and Rogue) get busted, the giant fiendish spider wades into the fray, and multiple spellguards (one copying the tactic of using Fly/Improved Invisibility they saw the party sorcerer use before the party was pushed back the first time) open fire, starting with Dispel Magic and Web. The party does ok overall as far as saves go, but the Paladin in heavy armor doesn't, falls, and gets stuck on the strands, as the spider enters melee with the rogue and druid. The Rogue lasts one bite before getting massively poisoned and running for it, and joins the fight against the drow - the Druid lasts a while longer, thanks to immunity to poison, but his Repel Vermin spell doesn't penetrate the spider's SR, and he too retreats.
Meanwhile, the Cleric and the Sorcerer are holding out reasonably well - the Cleric wades into combat, joined soon by the Rogue whose Strentgh he boosts back up, and the Sorcerer moves out past the periphery of the web and starts slinging spells...
A long exchange ensues, during which the spider is killed - but not before reducing the Paladin to 0 Strength with his poison, most spells are expended on both sides, and one of the drow casters dies, along with several of the elite guards. It looks like the party's going to triumph, but one of the drow casters throws a Polymorph Other at the Sorcerer as a parting shot before retreating - and the Spider Climbing Sorc gets changed into a trout, plummets down (not hitting the strands because he moved away from the web) and ends up at -40 or so hit points... And the party is forced into retreat yet again by the unexpected set-back.
Tune in next week, when the party resurrects the sorcerer, and teleports into one of the openings they observed during the combat, which turns out to be the main guard barracks...