I hope he'll return safely
Only he was developing the game, so there's only one copy of the game's source code, which makes further development impossible.
In fact, the lead artist I mentioned had considered redesigning the game, but it would require a lot of money. Currently, no one can edit the itch.io page or access the funds on Patreon. Moreover, asking for donations before confirming whether he is still alive isn't appropriate.
The substitute is the manga I mentioned, which will continue and conclude the game's story.