وَإِن مِّنْ أَهْلِ الْكِتَابِ إِلاَّ لَيُؤْمِنَنَّ بِهِ قَبْلَ مَوْتِهِ وَيَوْمَ الْقِيَامَةِ يَكُونُ عَلَيْهِمْ شَهِيدًا (4:159)
4:159 (Picktall) There is not one of the People of the Scripture but will believe in him before his death, and on the Day of resurrection he will be a witness against them
According to this verse of the Quran Jesus will be coming back and in his second coming some of the Christians will witness his second coming. Muslims believe as God told us in the Quran is that Jesus did not die on the cross like some of the Jews conspired to do that but raised him to himself. We do not know if this aescent was with both the spirit and body or only the spirit to know that we have to have revelation. To my knowledge there is no indication from the Quran or Sunna of either. The most relevant to us is he had ascended and he will come back to establish the kingdom of heaven.
According to a lot of prophecies observers we are at the end of time before his second coming. One of these signs is a guy like me write to himself in a closed confinement and people from around the world waiting every thing he write. Of course the tyrants of the world wish we are not in the end of time and they will continue to enjoy their evil. Time out, we are in the end of time. Since the meek will inherit the earth the time of tyrants will be soon over.
Some Christians think that they will ascend in the rupture to meet Jesus in the air. Muslims believe no one is going up we all will go through the tribulation and he will descend between us. when he comes down he will establish the kingdom of God. He will live and die like other prophets and like us and even will have a family. Thus in his death which have not happened in the first coming in Quran mentioned as wafa or taking back and not real death unlike the verse mote above which indicate the real death after his second coming.
Thus some of the Christians will witness his death and all of Christians in the day of judgement he will be witness on them, that he never said he is God or he should be worshiped. See these verses describe this scene in the day of judgement:
وَإِذْ قَالَ اللّهُ يَا عِيسَى ابْنَ مَرْيَمَ أَأَنتَ قُلتَ لِلنَّاسِ اتَّخِذُونِي وَأُمِّيَ إِلَـهَيْنِ مِن دُونِ اللّهِ قَالَ سُبْحَانَكَ مَا يَكُونُ لِي أَنْ أَقُولَ مَا لَيْسَ لِي بِحَقٍّ إِن كُنتُ قُلْتُهُ فَقَدْ عَلِمْتَهُ تَعْلَمُ مَا فِي نَفْسِي وَلاَ أَعْلَمُ مَا فِي نَفْسِكَ إِنَّكَ أَنتَ عَلاَّمُ الْغُيُوبِ (5:116)
5:116 (Picktall) And when Allah saith: O Jesus, son of Mary! Didst thou say unto mankind: Take me and my mother for two gods beside Allah? he saith: Be glorified! It was not mine to utter that to which I had no right. If I used to say it, then Thou knewest it. Thou knowest what is in my mind, and I know not what is in Thy mind. Lo! Thou, only Thou art the Knower of Things Hidden. -
مَا قُلْتُ لَهُمْ إِلاَّ مَا أَمَرْتَنِي بِهِ أَنِ اعْبُدُواْ اللّهَ رَبِّي وَرَبَّكُمْ وَكُنتُ عَلَيْهِمْ شَهِيدًا مَّا دُمْتُ فِيهِمْ فَلَمَّا تَوَفَّيْتَنِي كُنتَ أَنتَ الرَّقِيبَ عَلَيْهِمْ وَأَنتَ عَلَى كُلِّ شَيْءٍ شَهِيدٌ (5:117)
5:117 (Picktall) I spake unto them only that which Thou commandedst me, (saying) : Worship Allah, my Lord and your Lord. I was a witness of them while I dwelt among them, and when Thou tookest me (in the first coming) Thou wast the Watcher over them. Thou art Witness over all things. -
إِن تُعَذِّبْهُمْ فَإِنَّهُمْ عِبَادُكَ وَإِن تَغْفِرْ لَهُمْ فَإِنَّكَ أَنتَ الْعَزِيزُ الْحَكِيمُ (5:118)
5:118 (Picktall) If Thou punish them, lo! they are Thy slaves, and if Thou forgive them (lo! they are Thy slaves). Lo! Thou, only Thou art the Mighty, the Wise. -
قَالَ اللّهُ هَذَا يَوْمُ يَنفَعُ الصَّادِقِينَ صِدْقُهُمْ لَهُمْ جَنَّاتٌ تَجْرِي مِن تَحْتِهَا الأَنْهَارُ خَالِدِينَ فِيهَا أَبَدًا رَّضِيَ اللّهُ عَنْهُمْ وَرَضُواْ عَنْهُ ذَلِكَ الْفَوْزُ الْعَظِيمُ (5:119)
5:119 (Picktall) Allah saith: This is a day in which their truthfulness profiteth the truthful, for theirs are Gardens underneath which rivers flow, wherein they are secure for ever, Allah taking pleasure in them and they in Him. That is the great triumph.
If you notice it is a win/win for Christians to those who did not know or were mislead there is forgiveness when they were sincere but wrongly took him as a God. For those who are well informed by Muslims he is a prophet and not God or son of God and they followed him in this way. Thus the most important is sincerity to find out and sincerity to follow. To know the tuth and you deny it is very worng in the eyes of God.