I wouldn't necessarily assume player ghosts in Demon would be identical to DCSS ones, for the record. If I've learned anything from working on this game it's that no matter how well a thing works in a very similar game, it may not work nearly as well or even at all in an even slightly different one, much less a markedly different one (see also: the ancient era of Demon where I still had stairs and you could backtrack )
The only thing I would assume to be true of a player ghost implementation in Demon is that it will involve encountering enemies that are, in some way(s), based on previous deaths by players. An exact copy of them? Maybe, if that works and feels balanced. If it doesn't work and isn't balanced, then it would be something less direct than an exact copy. To be clear, DCSS ghosts are hardly exact copies either if I recall the rules they use properly.