Happy Gilmore
If Happy wasn't already in jail for attacking his hockey coach, after throwing a government employee through a glass door down a flight of stairs he most certainly would have been imprisoned...End of the movie.
The Boondock Saints
The Russian mobster would have shot the McManus brothers in the loft...End of the movie.
Home Alone
Not that I need to say it but I will anyways. Let's try not even fathom the idea of an entire family forgetting a member of it and look past that two adult thief's didn't just shoot Kevin. If he made it to the end of the movie Kevin's parents would be turned over to child services, preventing sequels...End of the movie.
The Dark Knight
The last of The Jokers henchmen would have just shot him in the bank...End of the movie.
The Notebook
Allie never would have written the "notebook" because she has Alzheimer's...End of the movie.
Reservoir Dogs
With the amount of blood coming out of Mr. Orange throughout the film, he would have died from blood loss shortly after arriving at the warehouse...Not ending the film but definitely taking out the twist and preventing the big ending shoot out.
Cheaper by the Dozen
The Baker family would have gotten a television show on TLC along side with Jon and Kate Plus 8, ridding of their need to move for Tom's new job...End of the movie.
Titanic
Jack would have lost the card game, never winning the tickets...End of the movie.
Half Baked
They would have stayed in and ordered a pizza...End of the movie.
Back to the Future
The Libyan terrorists shoot Doc Brown and Marty...End of the movie. (Unless Einstein drives the DeLorean)