Before I have an angry mob beating down my door for slandering one of Disney's most beloved franchises (and my own), allow me to plead my case. The lionesses could have and should have ousted Scar without Simba's help. But I know what most of you are thinking: Scar is the king, the hyenas have the advantage in numbers, and Simba is still alive, so why would the lionesses revolt? Well, mainly because those reasons don't mean anything.
Take Scar. Let’s be honest: the lionesses only abide by Scar's rules for mating purposes. As disturbing as that sounds, Nuka, Vitani, and Kovu are proof that Scar took his lineage seriously. There's even a deleted scene from The Lion King that’s included in the stage musical in which Scar tries to seduce Nala (spoiler: it fails epically). Scar is a terrible leader—sociopathic, arrogant, and foolishly stubborn. He turns Pride Rock into a barren wasteland and makes a devil’s agreement with the hyenas. Considering these factors, it's a wonder the lionesses don't try something. Kill Scar. Banish him. Create an Amazonian society and if they really need a male, either wait for Nuka and Kovu to grow up or find another pride with an excess of male lions. If Mufasa and Scar’s relationship is any indication, presumably it's normal for a king to allow other males stay in a pride.
The next logical step is to handle the hyena situation, which should be pretty easy. All the hyenas are weak from starvation and none of them are happy with Scar's reign. Though they outnumber the lionesses, the hyenas are more synchronized in their singing and marching skills than they are at fighting. Rafiki takes out eight of them in ten seconds. Speaking of which, if the lionesses are really worried about the numbers, then enlist the aid of the rest of the animal kingdom. According to the Circle of Life, the animals are perfectly happy celebrating the prosperity of their future predator, so it's doubtful any of them actually want Scar in power.
And it's not like they're expecting Simba to return, either. They all think he's dead, so if the lionesses seize Pride Rock they're not consciously taking what’s his. Even when Simba returns, he's sort of useless. The weatheris more effective than Simba. What does he do? He talks, fights hyenas for an extremely short amount of time, and then faces off against Scar. Simba is a weak fighter; Scar is even worse. I don't care if you're the chosen one or the one true king—if you've spent the past ten years eating nothing but bugs and berries and doing absolutely no physical training, you are going to be as competent as a novice attempting to play "Flight of the Bumblebee." And if Scar is afraid of fighting Simba, what does that tell you about Scar's fighting abilities? There's a reason he needed an army of hyenas to master the courage to face Mufasa, and all Scar did was not hold onto Mufasa's paws.
Here's the situation: the lionesses literally have no food, no leadership, nothing to lose by usurping Scar. Kill the king or exile him. Find another pride and steal a male lion, or become the first lion sorority in Africa. Defeat the hyenas. Get the herds back. If Simba through some divine intervention returns to Pride Rock, then he can find Queen Nala lounging by the water hole with a mountain of food and asking Zazu, "Simba who?"