So, you want Dante to kill them? Devil arms are their souls, you know that right?
It doesn't kill them, though. DMC3 Cerberus, Agni & Rudra, and Balrog all willingly become weapons without actually being slain, and the latter two retained their awareness of the world and their ability to communicate. Admittedly Agni & Rudra were already weapons, so they sort of don't prove anything, but it's even been officially stated that Devil Arms retain their identities when transformed into weapons, they don't die, nor is it a requirement that they be slain.
Finally someone add them to danbooru, didn't know the artists cbreturn here known as Caibou
Because caibao is a Pixiv stacc name, not the actual name used by the artist. Hold up, let me fix it. Edit: sorry, can't do it by myself. 107 posts. Edit2: caibao is partially correct, only missing "return" part.