Well, here's all you need to survive the encounter with the Spineback Basilisk, my friend! - It's a little thing called Dazzling Flame, Level 6!!
That's right! - With Dazzling Flame, Level 6 spell, you'll be able to keep the Basilisk at bay for a couple of turns, while you continue to "soften" 'im up with some Level 6 Fleshboil spells! (I assume Spark will also work, though I didn't try it; and I've got to assume that Sunder Flesh, Mystic Hammer, Ice Lance, and the like, will also work on the Basilisk...)
Now, the Spineback Basilisk is pretty good even with Level 6 Dazzling Flame, so he'll turn back at ya every 2-3 turns or so! - But just keep switching off between the Level 6 Dazzling Flames and the Level 6 Fleshboils, and you'll get yourself out of that "Pit", in no time!!
(But don't forget to "pre-open" those gates in Atrox before you do, or you'll be trapped in with that madman in the cell for all eternity!!!)
Easy as pie!!

And that, my friends, is why Dazzling Flame is always a good spell choice!...



(P.S. Totally aside, here - Has anyone else figured out what the whispering voices on the soundtrack say when you're in Atrox Deep?! I think one of them says something like "I'm starving in here!", but I'm not sure what any of the other whispered soundtrack voices say... Anyone know?)