As I see it there's a few reasons to attend a JC for apostasy, and keeping your family is probably one of the smaller ones. In my mind the only thing to do if you want to keep your family is to go and lie your ass off in an attempt to prevent being DFed. Going and arguing with elders and deciding whether you claim the WT is wrong vs god doesn't exist - none of that really matters because you'll be DFed and your family will shun you (often without fully knowing why anyway, so it doesn't matter if you're athiest or just non-JW christian).
For those that go and argue the point with the elders, there's a couple reasons I can think of. 1st is probably the misguided attempt to wake them up. I say misguided because I don't think I've ever heard a story of a former elder here relating how they woke up after sitting on a JC for apostasy. I'd love to be shown wrong, but I doubt that's happened anywhere near enough times to justify the effort.
Next possible reason would be seeking validation. In some cases this might fall into a subset of the first reason, i.e. you think you're going to be validated by waking up an elder in the JC, but I think in most cases it's to go and make airtight arguments that the WT is wrong and see the closed-minded iron-fisted elders fight back using dirty tactics, excuses and fallacious arguments. I can see this being validating because you'd leave knowing that you're absolutely right if their best is truly that pitiful. Another way it could be validating is to see that these elders, in spite of what they might say, are not seeking to save a lost sheep as they are supposed to according to the bible. They are seeking to expel you, further proof of the unloving, unchristian policies of this cult.
Then the best reason I can think of to attend a JC - to record it and post it online as a way of demonstrating just what this cult is really about. The more publicity this nasty side of the cult gets, the better.
Maybe I've missed something, but I really can't think of any other goal that you could possibly hope to achieve by attending your JC. That said, I will never attend a JC. I'll probably be DAing at some point in the not-too-distant future.