I mean, if the game was leaked wouldn't it show up all over the forums? [The spoiler threads themselves, not the spoiler warning threads]. In addition, the only "spoilers" we've seen are confirmed to be fake title screens and gameplay of one map that very well could have been from another build.
TL;DR: If it was spoiled, you'd have heard about it by now.
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How did 343 react about the leak? That's the biggest question. Someone leaked Bungie info once. They fed him into the dreaded soul extraction machine for it. Has 343 demanded anyone's soul yet?