Nowadays, the gods are not necessary. For Clerics and Paladins, you can say that they derive their power from faith in an ideal, philosophy or cause. Certainly, I would have assumed that you can provide a similar god-free answer for Druids, even to a GM whose setting is the strictly canonical FR.
There is a difference of opinion within WotC on this issue. When Greenwood is asked if the need for a god and the related fate of the faithless and the false are still in place he says yes. In the realms everyone needs a deity or they are going to suffer in the afterlife. (and if you have an evil deity you are still going to suffer) The idea that you can worship an abstraction like "law" only exists in settings like Ebberon, Dragonlance and Greyhawk.
I take Greenwood as the final authority on these matters. He's contributed more to building this world than anyone else.
Now if were DMing and someone wanted to play someone false, faithless or atheist-despite-all-evidence I would let them. The point of the rules is to have a stable place from which players can deviate, the rules illuminate the crystalline structure of your unique snowflake. So if Larian wants bring a home rule that allows people to choose no deity or an abstraction I'm all for it as long as the strangeness of the decision is highlighted. A note should appear on the character maker screen and NPCs should comment on it.
. . .
Shadowheart: "You know those fine words won't sway Kelemvor's heart or move his hand, right? He judges the dead without passion or prejudice. He will either let your soul dissolve in the wall of the faithless, give you over to some devil or declare you a worshiper of some god you once mentioned in passing"
Tav: "He can't assign me to some god just because I said their name once"
Shadowheart: "He can. He's the lord of dead, it's his decision. Besides, he'd be right to do so. All of us engage of acts of worship whether we realize it or not. When we ask Tymora to smile on us or implore Beshaba to avert her gaze we are actively venerating the gods.
You need to choose a deity. It's the only thing that makes any sense. In the mean time I would choose your next curse words carefully. I wouldn't want to see you stub your toe and hand your soul over to the goblin god of latrines or something worse.
