Asleep in Christ?

In the reading on page 192 I found it interesting that Polhill states that the Thessalonians were probably not doubting the eventual return of Christ, but were more worried about the place the dead would have in the events surrounding the return. It seems like a logical concern but at the same time as I am coming from a background of being taught the belief that to be absent from the body is to be present with God. I have not searched scripture on this and it makes me think about it more because I have in the past just trusted this as fact from the things I have been taught. I will have to look for the basis on this, but if it does come from scripture then I find myself asking why didn't the Thessalonians know about it unless it is from the new testament writings. I really need to search this out better but this is my first thought after doing this reading and it kind of makes me question this that I have taken as fact which is probably a good thing that will give me motivation to study on it more.