The entire reason littlefinger's plot failed is because of theon and jon.
Littlefinger successfully fucked the starks, stannis and tyrells due to his fuckery.
If theon didn't help sansa escape and jon didn't come back and fight, littlefinger had already planned to wipe out the boltons with the vale with cersei.
The idea was he'd consolidate control of the north with that move. But the starks messed that plan up which forced him to try to politick his way into victory.
That's why if jon and theon plot didn't happen, littlefinger was just cersei's death away from the iron throne.
Hmm thats right, I felt like that plotline ran for way too many seasons until the present day in which I forgot why he was even scheming in the first place? Totally forgot about his ambitions to become warden of the North.