If sinners Christ died for still die in unbelief,it would contradict the very purpose of mercy. See God concluded all His Chosen People in Unbelief ! And what for ? This scripture tells us Rom 11:23
For God hath concluded them all in unbelief, that he might have mercy upon all. Now whose the All ? Why he told us in Rom 9:23-24
And that he might make known the riches of his glory on the vessels of mercy, which he had afore prepared unto glory,
Even us, whom he hath called, not of the Jews only, but also of the Gentiles?
God in His Eternal Purpose in Christ, enclosed the His elect into unbelief, so that, for the purpose of being able to show them mercy, compassion in that state of unbelief/disobedience, not to condemn them for it, as many false teachers teach today, that God condemns sinners Christ died for, for unbelief ! Thats the biggest lie ever told !
Paul is an example of how God has mercy upon His Elect for their unbelief. Remember Pauls testimony of all what he did in unbelief 1 Tim 1:12-13
12 And I thank Christ Jesus our Lord, who hath enabled me, for that he counted me faithful, putting me into the ministry;
13 Who was before a blasphemer, and a persecutor, and injurious: but I obtained mercy, because I did it ignorantly in unbelief.
Paul as all other Vessels of Mercy, obtain, receive mercy in their unbelief ! Thats what Paul means in Rom 11:23
For God hath concluded them all in unbelief, that he might have mercy upon all.
Paul was not broken off because of Unbelief as many other jews were his contemporaries Rom 11:20
Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear:
But Paul along with other Vessels of Mercy, not just among the jews, but also among the Gentiles Rom 9:23-24
And that he might make known the riches of his glory on the vessels of mercy, which he had afore prepared unto glory,
24 Even us, whom he hath called, not of the Jews only, but also of the Gentiles?
So its not even possible for those whom Christ died should die in or be condemned for unbelief, their unbelief obtains the Mercy of God upon them !