To die as a believer in Christ is to exit this mortal coil and be with him eternally in the great hereafter. To die with disbelief is to not be with him, and to not be on Earth either. You wanna know what I think happens to them? I don't know - all I know is what I know and all I know is that I believe Christ died for everyone's sins - that means everyone - and that all it takes is accepting that he did just that and believing that he died for all of us and that will open the gates to eternity for all who do believe. I couldn't tell you what hell is, or what it's like, but I'm certain it isn't good.
It's a scary topic no doubt, I was an Atheist for nearly half of my life (most of my young life), and I still have friends and family who are Atheists. When I die I want to be able to see them again, and it tears me to shreds imagining that I won't be able to, that I might not be able to convince them otherwise, that I might not be able to get them to see the beauty of the things that I can see.