"It is better for you to enter the kingdom of God with one eye, rather than having two eyes, to be cast into hell fire—where 'their worm does not die, and the fire is not quenched'" (Mark 9:47-48 Mark 9:47-48  And if your eye offend you, pluck it out: it is better for you to enter into the kingdom of God with one eye, than having two eyes to be cast into hell fire:
 Where their worm dies not, and the fire is not quenched.
American King James Version×).
The quoted phrase "hell fire" is translated from gehenna—the Greek form of the Hebrew Gai Hinnom, meaning Valley of Hinnom, which was just outside Jerusalem. In Jesus' day this area was a garbage dump in which fires burned constantly, fueled by trash and the dead bodies of animals and criminals.
Jesus used this desolate and miserable place to represent the fate of unrepentant sinners. Notice that Jesus said the worm does not die, not that the people punished in hellfire do not die. The punishment is eternal, meaning that it is permanent and complete. But this does not mean that the incorrigible are kept alive perpetually and tortured incessantly by a vengeful God.
Burned remains of the bodies in theoriginal gehenna, the Valley of Hinnom, decomposed and were infested with maggots. The fire was not extinguished—it burned as long as there was trash to keep it burning—and the maggots (the "worms" of Mark 9:48 Mark 9:48Where their worm dies not, and the fire is not quenched.
American King James Version×) were not destroyed. Maggots are the wormlike larvae of flies. Flies swarm over the decaying refuse and keep it continuously infested with maggots. Then, instead of dying, those creatures turn into more flies in a continuing cycle.
The bodies of animals and people thrown into gehenna, however, either decayed or burned up and, of course, were eventually completely consumed. Similarly, unrepentant sinners will not be tormented forever. Quite the contrary, they will be completely and eternally annihilated in the lake of fire, referred to in Revelation 20:14 Revelation 20:14And death and hell were cast into the lake of fire. This is the second death.
American King James Version×.