Friday the 13th: The Final Chapter was billed as the last entry, and Jason's original demise would have made the slasher's return in future sequels impossible. Despite their robust success at the box-office, Paramount was always a little embarrassed by the Friday The 13th movies and planned for the fourth movie to end the series for good. This involved giving Jason a suitably gruesome death, the details of which constantly evolved throughout production.
Friday The 13th: The Final Chapter also introduced series favorite Tommy Jarvis, a young boy who is forced to confront the killer in the finale. Young Tommy is shown to have a talent for amateur special effects, and before the showdown cuts his hair and applies make-up to make himself resemble young Jason. This allows him to get close enough to deliver a killing blow with the slasher's own machete, which includes the memorable image of Jason's impaled head gruesomely sliding down the blade. However, the original death of Jason would have made his resurrection in Friday The 13th Part VI: Jason Lives nearly impossible.
In the 2013 documentary Crystal Lake Memories, Friday The 13th: The Final Chapter director Joseph Zito recalled the numerous ways the crew thought about killing Jason. Most of these ideas were presented by Tom Savini and his effects team, but Zito felt many of them were too complex or "clever" for the sake of it. Savini himself recalled one serious consideration saw Tommy jam a handmade gadget into Jason's head and frying him with a strong electrical current until his head exploded.
Zito confirmed this concept was taken very seriously for a time by producers, but it was eventually discarded. Instead, the director decided that it would poetic for Jason to be undone by his own weapon, which is how Friday The 13th: The Final Chapter now ends. Also of note is that initially, Jason’s head was going to be split diagonally from top to jaw, but the studio requested that this not be done. It’s at this point some in the team suspected the studio could be leaving a door open for another sequel.
Ultimately, the ending of Friday the 13th: The Final Chapter is one of the most memorable of the series, and the sight of Jason sliding down his machete caused audiences to cheer back in 1984. Of course, the huge success of the "final" movie spurred Paramount to make another, with Friday The 13th: A New Beginning featured a copycat killer instead of Jason; the ending also strongly implied Tommy would become the franchise's next killer. The fifth movie was another hit but following a backlash to the copycat reveal, Jason Lives delivered on its title by bringing the slasher back to life. In this case, the studio was probably glad of their call to not explode Jason's head.