Most people who abandon Christianity, abandon it mentally for some kind of Christianity-lite.
The famous Richard Dawkins is an obvious example of this (and even confesses at times to being a "Christian atheist"). Lorry-loads of Christian assumptions and aspirations, which he mostly takes for granted, remain embedded in his thinking and mode of operations. For some reason, he still feels that he needs to justify his existence by crusading to convert everyone to The Truth - even though "The Truth" (for him) is that soon, we're all nothing, and that the ultimate meaning of that is that there is no ultimate meaning to that. A strange thing to get so worked up about, isn't it?
Consistent atheism would be absolute nihilism - but human beings and the created order they live in aren't wired for that at all, so consistent atheism is impossible to find in reality. Reality isn't meaningless, and human beings aren't luckily-rearranged offspring-of-pond-slime who are heading towards eternal nothingness.
On which note, this link: http://triablogue.blogspot.co.uk/2014/09/what-if-im-wrong.html, which leads in turn to this one: http://www.proginosko.com/2013/08/the-atheists-guide-to-reality/