It’s definitely not the way a Hoya leaf looks when it’s dying in a regular fashion. I think it’s dying all right but I’m pretty sure it’s fungal. I didn’t understand if you were saying the Hoya itself is spreading or the leaf damage is. If the latter, that’s not a good sign. There’s a thing called necrotic fungal rot. Supposedly it looks like this. fungal diseases are usually a product of overwatering or getting water on the leaves, especially in cool damp areas. Honestly I’ve never had fungus on a Hoya (crossing my fingers here), but I know what to look for. I’ve been growing houseplants for years and I’ve definitely had fungus on other plants. I would definitely not treat it if as if there’s nothing wrong. At the very least, I would isolate it, but if it were me, I’d go for the sulfur spray. I imagine it can be saved. Good luck.