Tricky. There are quite a number of duergar there and you hardly have area effect spells.
Don't use the slow, use the skull trap instead. But only once they can all be affected by it. Then use orb and orb on the two most dangerous remaining duergar, followed by either another orb or the missile, your drain and your arrow. You'll probably have a sling to do some damage once the real threat is gone, but if things go badly just use spook on one and run, then rest.
I know you don't want to, but there's nothing wrong with a bit of sleep sometimes.
Are you soloing a sorceror on insane without reloading and a maximum of ten rests? Impressive [img]smile.gif[/img]
EDIT: Oh, yeah. Get an invisibility next time you level so you can sneak past the baddies you can't really handle