The ideal setup for story lanes (diverging paths from a linear narrative) IMO is to explore three levels of plot, personal plot explore the connection between the player and the character, the cast plot which introduces and exits other characters and their impact on each other and lastly the strategic plot which is the win or lose condition at the end of the game (Western Cultures tend and trend towards the strategic win condition plot lines instead of the lose condition though these can be more artistic, other cultures vary). The connecting moments between each of these three layers is what sets the pace for the story (for example driving the story forward or edging slowly towards and dramatic moment) and creating a level of mystery in one layer means you need to offer answers in another to keeps a player connected to the plot.

The first layer is the easiest to stray from (creating branching moments) the other two layers because personal challenges are the most rewarding and players are selfish enough to justify ignoring the plot line if it means personal growth (aka grinding...gross). The second layers choices need to connect the player to aspects of the third layer no matter what the choices outcome otherwise it feels like fate holds the reins and players lose their sense of accomplishment. Only add characters that matter because getting rid of (killing, disappearing, etc) useless characters feels useless to the story. The last layer is best explored with only as many endings as the main character has meaningful emotional or physical attributes the player will care about (for example, if you've told the player the character is 1.an orphan 2.blind 3.a mage fated for greatness 4.a bad ass with a heart of gold then stick to 4 endings) and the player should never expect the moments that define which of these endings will be chosen.

This is the way I approach my RPG or cross-genre game stories since it ensures that anything I add to the story is either first layer gameplay related or 2/3 layer requirements of the story with no filler or fluff, just the essentials.