We are trying to find out what exactly happened to Jesus, and trying to understand what exactly this conjecture occured about him. Quranic information about Jesus' crucifixion is not explaining every detail, in fact Quran doesn't say many things about Jesus's life.
About crucifixion, it just simply says the situation was not like people knew until the quranic revelation saying about ambiquity of the situation, came to Muhammad (pbuh). If someone else would have been put instead of him, Quran would have no reason not to mention this person, to give an end to all those debates and conjectures.
Beside, We see in quran 3.56:
Remember the time when Allah said, 'O Jesus, I will cause thee to die a natural death and will raise thee to Myself, and will clear thee of the charges of those who disbelieve, and will exalt those who follow thee above those who disbelieve, until the Day of Resurrection; then to Me shall be your return, and I will judge between you concerning that wherein you differ.
seems to me as a message that Jesus will be saved from such a death, but he will be given natural honourable death. It probably points that Jesus continued his life after survival from crucifixion, until a natural death came upon him.