There are three main beliefs within Christianity:
Some believe that the rapture will occur before the rise of the Antichrist and the events described in Revelation (note the singular).
Some believe that Christ will call home the faithful midway through the strife.
Some believe that only those who are faithful for the complete event will be called up.
I haven't read the book myself in a while, but I do remember being told about these three schools of thought, as it were.