While it’s not impossible, I don’t see Malthael returning, at least not as he was before. Unlike Demons whose resurrection only result in a change in appearance (as such they’d be the same demon with only a different look), angels resurrection result in a change in identity; the only known exception to this was Tyrael, as after he destroyed the World Stone, his physical body was destroyed, but he resurrected two decades later as the same angel. However, I doubt the same would happened for Malthael if he was resurrected, he’d likely be a different angel with the only similarity to his former self being their essence.
On the other hand, if Malthael’s essence were corrupted and perhaps demonized just as Izual was (which wouldn’t be impossible considering Malthael destroyed the Black Soulstone in order to absorb the Prime Evil’s essence into himself), then it’s very possible that Malthael may return as well as a corrupted angel and undergo a demon’s resurrection just as Izual did.
Unlikely as the playable characters and classes in Diablo have always been Human/Nephalem. As such a reaper, and by extension angel, class wouldn’t fit with that as they would lack the demonic essence that humans possess; unless you’re talking about a class that could draw forth the power of angelic beings, including reapers, and make it their own.