That was my assumption. Artistic license, having all the body decay away to the skeleton, but the skin and sinew on the face is more or less intact in its death rictus. *brrrr*
Ohhhh yeahhhh. *brrr* I think I blocked that out of my memory self-protectively!
I suppose we consider that a "failed" troll transformation because it (apparently) died of its own accord? While I don't think we've had a consensus on whether trolls and Rash-Beasts ever die "naturally" (Cthulhund seemed at the end of its rope, but who knows what might have happened if Emil hadn't intervened), my thought is that they're probably more or less immortal until or unless some external condition intervenes -- freezing, lack of nutrition, getting shot/flamed, etc. (This is based on my headcanon that the Rash was started by an ill-thought-out attempt to overcome aging by trying to strengthen
cell telomeres; the formula worked in some ways, so infected cells are essentially deathless, but they've gone very wrong indeed...)