Hell is the place of the dead. What happened was somewhere somehow Christians portrayed it as a place of suffering. Either that would mean it was temporary and then everyone is cast into the lake of fire or they had a weird eschatology that believed hell was the final destination of the unbelievers.
However one does not need to mistranslate a word as hell to see that the bible speaks of a final destination/state of punishment
I posted them already from Mat,
Mat 24 and 25, the Lake of fire. It's mentioned quite extensively. Gehenna seems to be a symbolic reference to it
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Mat 5:22 But I say to you that everyone who continues to be [30] angry with his brother or harbors malice (enmity of heart) against him shall be [31] liable to and unable to escape the punishment imposed by the court; and whoever speaks contemptuously and insultingly to his brother shall be [32] liable to and unable to escape the punishment imposed by the Sanhedrin, and whoever says, You [33] cursed fool! [You empty-headed idiot!] shall be [34] liable to and unable to
escape the hell (Gehenna) of fire.
Mat 10:28 And do not be afraid of those who kill the body but cannot kill the soul; but rather be afraid of
Him who can destroy both soul and body in hell (Gehenna).
Mat 23:15 Woe to you, scribes and Pharisees, pretenders (hypocrites)! For you travel over sea and land to make a single proselyte, and when he becomes one [a proselyte], you make him doubly as
much a child of hell (Gehenna) as you are.
Luk 12:5 But I will warn you whom you should fear: fear Him Who, after killing, has power to hurl into hell (Gehenna); yes, I say to you, fear Him!