The eternal fire consumes whatever is put into it. That is what fire does. The eternal punishment is to be consumed by the fire.
Then it wouldn't be eternal.
Only the righteous go into eternal life. Those who are punished don't receive eternal life. This verse says "The righteous (go) into eternal life." The eternal punishment is to perish and be dead eternally.
Those who do not exist cannot be punished. It would not be eternal.
Your statement that "if true the NT wouldn't say eternal" is simply not true. God's Word does say that the wicked perish and are no more and the NT does say eternal.
Eternal is quite clear. Eternal life, eternal punishment, NEVER ending.
Eternal punishment in GREAT detail:
Luke 16:22-28 (NASB)
22 "Now the poor man died and was carried away by the angels to Abraham's bosom; and
the rich man also died and was buried. 23 "In Hades he lifted up his eyes,
being in torment, and *saw Abraham far away and Lazarus in his bosom. 24 "And he cried out and said, 'Father Abraham, have mercy on me, and send Lazarus so that he may dip the tip of his finger in water and cool off my tongue, for
I am in agony in this flame.' 25 "But Abraham said, 'Child, remember that during your life you received your good things, and likewise Lazarus bad things; but now he is being comforted here, and
you are in agony. 26 ~'And besides all this, between us and you there is a great chasm fixed, so that those who wish to come over from here to you will not be able, and that none may cross over from there to us.' 27 "And he said, 'Then I beg you, father, that you send him to my father's house 28 for I have five brothersin order that he may warn them, so that they will not also come to
this place of torment.'
He wasn't 'consumed'. He was quite alive in the fire.