The way that you said it implies that you think he's going to hell - and whether or not you tell him is irrelevant.
To answer the question, I have nothing against anybody's belief - Christian or otherwise. I have a problem with them forcing it on others and I have a very very big problem with preaching because it irritates the crap out of me.
Anyway it's only a matter of time before that ignorant dodo shows up on this thread so I don't think I'll be adding anything further.
Christian belief is that if you don't believe in Christ you will go to hell. Now there are loopholes and some churches, I can only speak about my own church (Roman Catholic - I don't know much details on this topic concerning other Christian Churches), actually leave it entirely to God ultimately, along the lines of even a non-Christian person can find Christ in his final hour, or
if a person who is non-Christian seeks a greater holy good - Christ may find him. There are also explanations for people who died before they could know Christ or died before He came or died in areas where missionaries never went to and aso on. I'm not a theologian so don't ask me the details

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Ultimately Catholics (speak for my church here) believe that God has infinite mercy, love and wisdom. We believe that ultimately He will not allow those people who through no fault of their own would not accept Christ, to be damned forever. We can also not judge what this failure of acceptance is either, whether it is wilful or influenced by peers, family, culture etc to the point that it becomes ingrained.
However even if Christian belief follows the lines of No Christ = No Salvation, why should it bother people who don't consider Christianity seriously or laugh it off as a fable? Say for example, I don't believe an ounce of what Jehova's Witnesses preach, and they preach that everyone but them will burn in hell,
but I allow them that point of view. I don't become depressed or angry because Watchtower magazine says I will burn in hell. I live my own life according to my own beliefs (granted these are influenced heavily by the Church, my parents, friends, culture, social laws of the country) but I don't become upset by those who don't believe in God and I don't become upset by those Christians who incorrectly believe Catholics worship idols (an example). I do however
wish that everyone would consciously believe in Christ. Wishing something and hating those who don't follow this wish are two different things entirely. So it makes me wonder why some atheists MUST belittle our beliefs or argue about them at every opportunity. Accept our beliefs and we will accept yours. As said we may accept but we don't agree with them, neither do
you have to agree with ours although we really hope you would.
Can Non-Christians be Saved?
http://www.catholic.com/thisrock/2004/0403sbs.asp
Do read the article above. It's most interesting.