This episode is brilliant in its writing and grim implications which may fly over some viewer's heads. I've already seen some confusion over certain details, and confusion soon turned to hate when these people couldn't decipher the answer themselves. Just to explain the whole Penny/Human Penny thing and why Human Penny didn't disintegrate:
The Spirit of the Staff of Creation can only create, not destroy. RWBY used this rule to their advantage by asking him to create a copy of Penny to contain the virus and all the mechanical part. This copy essentially was made with everything Penny IS, except the soul. Given he can't destroy, and thus not harm anything, the Spirit of Creation had to also build a vessel for the soul. However, given this vessel was NOT part of their wish, when they then asked their next wish, it was not destroyed, unlike the remains of Penny's robot body.
Essentially it was a loophole and a very desperate bet, but they knew that already as they admitted themselves. It was very clever. Loopholes with divine artefacts are always fun. Well he had to make sure she would survive in her new form. Since he cant destroy. It was decent of him to not make her a quadriplegic. But it makes sense since the characters knew from Oz that these Spirits are not malicious.