In the Forgotten Realms, Lolth recently fell silent for several months - her priestesses couldn't reach her, couldn't get spells, and all that. Even then, she managed to retain her status as prime deity - though several drow deities made attempts to overthrow her (Vhaeraun actually intended to go and slay his mother, but he was stopped - and in the wrong place, anyway).
There are already drow who don't follow her - in the Realms, the drow even have a whole pantheon, although of course her clerics keep the knowledge of these deities from the general population (the first step of keeping someone from joining a church is to convince him that the church doesn't exist).
But to turn all the drow away from Lolth would take either something big or a lot of time.
I could see another deity killing Lolth and taking her place as main deity of the drow. This could be a deity from somewhere else entirely (let's say, Erythnul, or the Realms' Cyric, got it into their heads to gain the drow as another force of death and destruction), one with more power than Lolth so they could defeat her in a more or less fair one-on-one (Cyric already killed a deity, and he's so chaotic that not even Lolth could predict his actions).
If you think of one of the Dark Seldarine, it would be somewhat more problematic, since they are all weaker than Lolth. I'd say Vhaeraun would have the best chances, since he already has a sizable following, what with all those males who got fed up with being lorded over by the priestesses, or those who wanted to make their fortune in the Night Above - without turning into some goodie nudist dancer like those Eilistraeeans.
He would probably have to increase his power and then get an edge to boot - maybe a big huge artifact, or turning his most resourceful follower into a proxy to outflank Lolth. Or something.
Turanil said:
My opinion is that those who are evil, always are neurotic, psychotic, more or less insane, etc.
Nah. In fact, it's something decidedly human to think about yourself first. You're taught sharing and all that, but the prime survival instinct is still there. And if then someone isn't taught helping others so they help you and what not, and may even be taught that his first instinct (thinking of himself first) was actually right, he might become a selfish bastard.
I don't call that insane.