Could the farm have functioned with both Snowball and Napoleon as leaders?
Snowball is the intelligence behind the revolution while Napoleon is merely power-hungry. Snowball has vision and ideals and seems to be sincerely devoted to improving the life of the animals rather than enjoying power for its own sake. Napoleon lacks imagination and is bitterly jealous of Snowball's ingenuity, so he begins to plot his downfall, the puppy dogs being his chief weapon. He also uses propaganda and gossip to convince the other animals that Snowball's expulsion is for their long-term benefit. Of course when he gains sole control, his lack of talent and vision soon becomes clear with disastrous consequences.
No, the farm could not have functioned with both of them because Napoleon's nature is so malevolent that it would be bound to erupt in violence at some stage.
The answer, in my opinion, is no. Without the pigs to lead them, the animals would have had trouble formulating plans. Without plans the farm work would have been very difficult.
Possibly, the animals could have made a go of it without the pigs, but I think the intelligence of the pigs served a critical role in the early success of Animal Farm.
This might not be successful after the dispute about the windmill. Both parties wanted absolute power. But even if either one of them rule animal farm, the farm will still not function well as absolute power corrupts. This can be suggested from the apples and milk incident.
No, the farm would have fell apart. Snowball reminds me of Brutus, and Napoleon reminds me of Cassius. Their revolution didn't turn out to well either.
Yes there are differences between thinking and approaches of Snowball and Napoleon. But except on the question of Windmill there is no indication in he story about Snowball being intellectually better than Napoleon.
I believe there are more similarities in them rather than differences. Both needed support of each other to lead the animals. Perhaps in the initial period of the animal rebellion both were genuinely interested in welfare of the animal, and subsequently both became selfish and power hungry.
The main cause of failure of Animal Farm can be attributed to the leaders becoming more interested in their own power rather than the welfare of animals. Snowball and Napoleon working harmoniously cannot solved any problem of Animal Farm as long as they work in their own interest at the cost of interests of other animals.