One of these possibilities: Nanobots. Like, what if there was a horde of nanobots inside Penny, in case something happened to her? They would swarm out and fix her back up within a short period of time.



Like, what if RWBY Volume 5 has an episode that takes place in Vale, where a small group of people make their way through the destroyed Colloseum in search for useful stuff (I mean, there´s lots of Dust there, which the battlefields were made out of), and then, suddenly, Penny stumbles out of a pile of debris. Sure, she looks a bit messed up, her synthetic skin being torn off at some places and all, but other than that, she´s fine. Mostly. Her weapon systems don´t work, so she has to use her swords normally (or just help with organisation and repairing, which shouldn´t be that much of a problem for her).



Or maybe Ruby still has one of Penny´s swords with her. Man, that´d be awesome if some Grimm knocks her away, she drops her scythe and it falls into some hard-to-reach place. Then Ruby just pulls a sword from whereever and makes short work of that Grimm.