rainsford sleep in zaroffs bed what can inferred

Rainsford's presence in the bed confirms Zaroff's death.

By killing a human Rainsford has gone down to the level that he believed Zaroff to be at, and then by sleeping in his bed we can infer that he has basically "turned into Zaroff". Rainsford turned into the monster that he dreaded the most, his hatred toward the general turned him into something he previously was not.