Sure, it's possible he could've passed away. But when one immediately jumps to that assumption, it speaks a lot about the individual. This is another human being we're talking about. Those with a sound mind would at the very least use levels of escalation in their train of thought, instead of showcasing a morbid mentality after a Dev goes (MIA) for 5 months. There's been other developers who's had health and mental issues and vanished for much longer than Nef has and have eventually returned without automatically being assumed "they're dead". The ghosting aspect in similar circumstances isn't exactly rare air when it comes to the Adult VN industry.
Sure there's been previous health issues, but for all anyone knows, the Dev could've just decided to cut ties with the community altogether. Could be just as much related to family issues, other opportunities, or just simply moving on with their life. Just wish for the best for the guy, throw in a wellness-check that isn't centered around "hoping he finishes this game", and find some other game to fap to. We have no idea what's going on in his life.