given the plot of 1985 hit Back to the future, how could Marty McFly have avoided having to reconcile his mother and father in order to save his life?

In 1985, teenager Marty McFly lives in Hill Valley, California, with his depressed alcoholic mother, Lorraine; his older siblings, who are professional and social failures; and his meek father, George, who is bullied by his supervisor, Biff Tannen. After Marty's band fails a music audition, he confides in his girlfriend, Jennifer Parker, that he fears becoming like his parents despite his ambitions.

That night, Marty meets his eccentric scientist friend, Emmett "Doc" Brown, in the Twin Pines mall parking lot. Doc unveils a time machine built from a modified DeLorean, powered by plutonium he swindled from Libyan terrorists. After Doc inputs a destination time of November 5, 1955 (the day he first conceived his time travel invention), the terrorists arrive unexpectedly and gun him down. Marty flees in the DeLorean, inadvertently activating time travel when he reaches 88 miles per hour (142 kilometers per hour).

Arriving in 1955, Marty discovers he has no plutonium to return. While exploring a burgeoning Hill Valley, Marty encounters his teenage father and discovers Biff was bullying George even then. George falls into the path of an oncoming car while spying on the teenage Lorraine changing clothes, and Marty is knocked unconscious while saving him. He wakes to find himself tended to by Lorraine, who becomes infatuated with him. Marty tracks down and convinces a younger Doc that he is from the future, but Doc explains the only source available in 1955 capable of generating the power required for time travel is a lightning bolt. Marty shows Doc a flyer from the future that documents an upcoming lightning strike at the town's courthouse. As Marty's siblings begin to fade from a photo he is carrying with him, Doc realizes Marty's actions are altering the future and jeopardizing his existence; Lorraine was supposed to tend to George instead of Marty after the car accident. Early attempts to get his parents acquainted fail, and Lorraine's infatuation with Marty deepens.

Lorraine asks Marty to the school dance, and he plots to feign inappropriate advances on her, allowing George to intervene and rescue her, but the plan goes awry when Biff's gang locks Marty in the trunk of the performing band's car, while Biff forces himself onto Lorraine. George arrives expecting to find Marty but is assaulted by Biff. After Biff hurts Lorraine, an enraged George knocks him unconscious and escorts the grateful Lorraine to the dance. The band frees Marty from their car, but the lead guitarist injures his hand in the process, so Marty takes his place, performing while George and Lorraine share their first kiss. With his future no longer in jeopardy, Marty heads to the courthouse to meet Doc.

Doc discovers a letter from Marty warning him about his future and rips it, worried about the consequences. To save Doc, Marty recalibrates the DeLorean to return ten minutes before he left the future. The lightning strikes, sending Marty back to 1985, but the DeLorean breaks down, forcing Marty to run back to the mall. He arrives as Doc is being shot. While Marty grieves at his side, Doc sits up, revealing he pieced Marty's note back together and wore a bulletproof vest. He takes Marty home and departs to 2015 in the DeLorean. Marty wakes the next morning to discover his father is now a confident and successful science fiction author, his mother is fit and happy, his siblings are successful, and Biff is a servile valet in George's employ. As Marty reunites with Jennifer, Doc suddenly reappears in the DeLorean, insisting they return with him to the future to save their children from terrible fates.

He could have not push his father out of the way when he fell into the path of an oncoming car.