I spoke with my OB yesterday, the pathology results were back in. My placenta was normal, one spot of degeneration, but she said that was probably post miscarriage and not a factor. Dominic was chromosomally normal, 46xy (male). He did have a clubbed right foot, but that had nothing to do with the miscarriage. So, basically, no obvious reason why his heart stopped beating.
I see my OB on the 25th for a "post-partum" check, and they'll run some tests on me to make sure there's nothing wrong on my end. But, she said in 60% of cases, they never find a reason for the miscarriage.
Not having a concrete answer doesn't really bother me. Sometimes things just happen, and I accept that. My biggest concern was a hereditary genetic problem, or something that could have been prevented/happen again. That doesn't appear to be the case, so that's a relief. Emotionally though I'm not in a place to get pregnant again any time soon. I feel like I need to get past his due date before I can even think about it.