Recently I was interacting with some Muslims about the longer ending of Mark 16. One Muslim on his web-site says that the longer ending of Mark discredits all of Christianity itself!
Christians are honest about the manuscripts, so that is actually a very positive point about the manuscript evidence of Mark 16:9-20. We have nothing to fear from the archeological and manuscript evidence. The evidence is positive for the OT and NT.
Mark 16:1-8 includes the empty tomb, the resurrection of Jesus from the dead, which includes the crucifixion and the necessity of His death - so, this is not a strike against Christianity itself. (and solid manuscript evidence of His trial and sufferings and crucifixion and death in Mark chapters 14-15)
6 And he said to them, "Do not be amazed; you are looking for Jesus the Nazarene, who has been crucified He has risen; He is not here; behold, here is the place where they laid Him.
7"But go, tell His disciples and Peter, 'He is going ahead of you to Galilee; there you will see Him, just as He told you.'"
8 They went out and fled from the tomb, for trembling and astonishment had gripped them; and they said nothing to anyone, for they were afraid. " Mark 16:6-8
The fact that the last few verses (Mark 16:6-8), which are not disputed, contains the testimony of the crucifixion, empty tomb, and the resurrection, should stop the mouths of those who want to cast doubt on the rest of Mark and all of Christianity, just because of Mark 16:9-20.
The death and resurrection of Christ are included in the rest of Mark (1:1-16:8), including Jesus' predicting his trial and death and resurrection in chapters 8-9; so it is valid and contradicts the Qur'an denial of real history (the crucifixion and death of Jesus Al Masih) in Surah 4:157.
Islam denies real history - in Surah 4:157, (but believes the miracle of the virgin birth of Christ, which Muslims affirm in Surah 19:19-21; Surah 3:45-48), whereas even liberal and skeptic and unbelieving scholars in the west like John Dominic Crossan, the late Robert Funk, John Shelby Spong, and Bart Ehrman ALL agree that the historical Jesus of Nazareth was crucified and died in history under Pontius Pilate, the Romans, and the Jewish council (Caiaphas, Annas, chief priest, scribes, Pharisees, etc.) around 30 AD.
Furthermore, the correct doctrinal content of Mark 16:9-20 is testified to and repeated in Matthew, Luke, John, and Acts. (the resurrection appearances and the Great Commission in 16:15 are in Matthew 28, Luke 24; John 20-21; and Acts chapter 1) The only questions in the Mark passage are about
a. appearing to them in "another form" (that may be another way of talking about Luke 24:13-33 and that they did not recognize Jesus until He opened their eyes.)
b. including baptism as he does in Mark 16:16 - even so, baptism is not included in the condemnation.
c. the part about tongues and snakes. (although God did do a miracle and protected Paul from the snake bite in Acts 28)
The rest of it is all orthodox (correct) in doctrine.
I asked this Muslim, "Have you read Dr. White's discussion of the longer version of Mark (16:9-20) in his book, The King James Only Controversy??" ( pp. 225-227 in the first edition, 1995) (He has a newer edition out which is even better)
Dr. White answers the questions that arise about this passage, and shows the evidence that many manuscripts that do contain the passage.
So, the issues of the longer ending of Mark (16:9-20) in no way takes down the rest of the Scriptures of the NT or the Bible, nor Christianity itself.
There are no real contradictions in the gospels; (they have all been answered) and there is no evolution from Mark to John, etc. That idea of "evolution" of the gospels and "redaction", etc. is an anti-supernatural bias against miracles and against God being able to speak and reveal Himself through prophets and books. Since Islam agrees with the truth of God, monotheism, and that He send prophets and books; Islamic apologists should not use arguments from liberals who operate from the same anti-supernatural bias.
The telescoping and including some details that other Gospels don't; and other writers excluding details are not contradictions, they are actually stronger evidences of a real eyewitness testimony, because if it was the exact same words four times, they would know that there was collusion. (as a detective or policemen know when investigating the historical circumstances of a case.)
In 1993, on a street in Istanbul, Turkey, during the month of Ramadan, one of my Turkish neighbors asked me, "why do you have four gospels? there must only be one Injeel!" (Injeel is the word for "gospel".) As we stood there at the intersection, and he spoke his broken English and I my broken Turkish, other young men began to gather round. I asked him, "what do you think? If there is a car accident here at the intersection; then, in a Turkish court of law, what is better; one witness on one corner, or one witness on each corner, making it four witnesses?" He paused and said, "Doru!" ("that's right!") "Dort tane daha iyidir!" ("Four of them are better!") Then he explained his new understanding to the other 10-15 or so other young Turks who had gathered around in curiosity. Then he asked me, "I would like an Injeel in Turkish, can you get one for me?" Yes, and I did. He enjoyed reading it in secret for about 3 months. Then his father discovered him reading it, pulled a knife on him (threatening), ripped it up and burned most of it. (he later told me) A few days later, one page of the Turkish NT (Injeel, "Incil" (In Turkish, the letter "c" is a "j" sound) was on my doorstep. It seemed to be a warning - "don't give the Injeel to my son!". My Turkish friend later also told me he was sad, because he enjoyed reading the Injeel; and that Isa Masih (Jesus the Messiah) was the most noble and sinless character he had ever read about. He said the Injeel was very different than what the Mollahs ("Hoca" - Turkish, pronounced, "Hoja") had said that the Christian Bible was about.
"How shall they hear without a preacher?"