i've seen a fair share amount of games go this way. good intentions and everything, eventually game development slows down to a trickle, and then eventually nothing at all. It seems many devs use the mental health issue which over the course of a number of years as become nothing short of a cliche for a lot developers out there.
This game's subscription model on supporters platforms should have been turned off completely while he was taking a form of sabbatical or whatever one wants call his time off, no way should he have been charging any subsciber anything given there was no update in over a year, that is inexcusable. If he did turn of subscription models during his entire break, good on him, more should be like that.
Anyway, yeah, I think this is the end for the game, it's clear he isn't well enough to continue or has enough time. he has personal issues that seem to continuously overwhelm his health. (this is not a critism, it's that this is his claim why he was gone for more than a year.) He needs to try and find other people to help him complete this game, but I am not sure how that might even translate that well to him. would he want others to help him, would he pay others to help him get his game complete? questions followed by more.
I wish him the best of luck anyway, mental illness is a terrible thing to have to go through and the damage it can cause others around those suffering too.