DS, my friend, let's be prudent because I still need you to explain soul sleep.
I don't think you need me to explain it because there is, after all, plenty of information about it on the internet. For example, the Wikipedia article on soul sleep (
here) is over 5,000 words long and contains a lot of information, both pro and con. And this is not to mention my suspicion that you're already informed on soul sleep because, as you indicated earlier, you're armed with philosophical critiques of it. That wouldn't be possible if you didn't know what soul sleep was. So, I think you're after something a little more precise than "explain soul sleep to me." I don't know but perhaps you mean something like, "What is your position on this question?"—which is something I could answer.
This is why I wanted you to submit a post on the issue (but within that existing thread because you can't start a post yourself just yet). You have a much clearer idea of where to start than I do. From my perspective, the range of possible discussions to be had is just too broad for me to successfully guess at what you're targeting and draft something on point. I was hoping you could submit a post describing the philosophical problems that burden the doctrine (as you understand it) and it could proceed from there. And, hey, if it turns out that your understanding of soul sleep is mistaken, even if only with respect to Adventist beliefs—for it is a bit unique—well, then you will have learned something new, and that's always a positive. Right?
If it helps, Adventists are physicalists of a sort. On their view, the human body is not possessed of an immaterial soul; rather, the human body just is a material soul. They would disagree with substance dualists, who hold that the mind is a feature of the immaterial human soul, while agreeing with property dualists, who hold that the mind is a product of but is not fully reducible to the material human brain (so it parallels but contrasts with reductionism).
So, it gets a bit complicated because, in one sense, they don't believe in soul sleep (since they reject the idea of immaterial souls surviving the dead human body) but, in another sense, they do believe in soul sleep (if we respect their belief that the human body is a soul). It's in the latter sense that they believe the redeemed who die are said to "sleep" (because they await a resurrection to eternal life) whereas the damned who die are said to "perish" (because they await a resurrection to eternal punishment). Keep in mind: Adventists believe in conditional immortality, and so that eternal punishment is annihilation (i.e., a death sentence that is forever).
By way of contrast, Martin Luther did believe in soul sleep in that Cartesian sense, that one has a disembodied immaterial soul that "sleeps" in the intermediate state, to be awakened by Jesus in the resurrection.
For me, it's hard to know whether Adventists and other soul-sleepers believe that "sleep" is a metaphor for death.
They believe that it's a metaphor for physical death in the same sense that Jesus did. When Jesus told his disciples that he was going to awaken Lazarus who had fallen asleep, they took it literally. So, Jesus had to tell them plainly, "Lazarus has died" (John 11:11-14; cf. 1 Thess 4:13-14).
If they think each mental event is a physical event, they're physicalists about the mind.
Yes, they are, but a physicalist is not necessarily a reductionist. So, I don't think the determinism critique follows. It might, I don't know, but at first glance it seems to target reductionism, a particular kind of physicalism.
By the way, I don't want to devote one to Michael Scheifler's theology.
I don't know what it means to "devote" someone to a theology, nor who Michael Scheifler is.
As for Adventists, it's a safe bet that they adhere to the fundamental beliefs of the Seventh-Day Adventist church, which can be found
here. (As for their beliefs about soul sleep, see "
Death, the State of the Dead, and Resurrection.")