@lapilofu: Try “he’s not hurting anymore” or “I’ll miss him” or some version of that. When someone dies it’s the same for the religious and the non-religious. We cry not for the dead but for ourselves because we miss the person. To the un-believer, the deceased is rotting or is ash or whatever the particulars of that death may be and he’s not hurting anymore. To the believer, the deceased has “gone to a better place” and he’s not hurting anymore.
The funeral is for the living and the most comforting thing you can do for the living is to be there while they’re hurting and missing the dead. Sometimes a reminder that we’re all hurting for ourselves, and not the deceased, is enough to get people through it. You don’t have to lie and say something you don’t mean, and you don’t have to point out your lack of belief while someone’s grieving.
On the original question, I use some of those phrase and don’t use others. Hell is just an idea of a horrible place to be stuck in so it can be appropriate in conversation as in “waitress from hell”, “line from hell”, “hotter than hell” and it makes the point.
I used to holler “Oh, God! Oh, God!” in bed, but I these days I give credit where it’s due instead. :^>