I understand you're coming from a compassionate place, you don't want to see them burn out, I've burnt out and it sucks.
You can make good money selling your time, but maybe it's not about money for them? By all other measures this game was a great personal success. At this point the dev is competent and successfully releasing games, they just haven't been commercially successful. Now would be a terrible time to give up.
My advice would be to run out of options first, then go work at that "elsewhere". Once you get settled into a career it can be really hard to step back out into solo dev.
I'm not going to refute the rest of your comment, as it's a valid opinion and I'd just be repeating myself, but in regards to this:
>Once you get settled into a career it can be really hard to step back out into solo dev.
I don't think that's true in and of itself. A lot of people struggle to adapt to the financial uncertainty of flying solo later in life, but that's only because they have a high-cost lifestyle and minimal savings.
I quit my day job last year, a few months before my first daughter was born, to run my online businesses full-time. The fact that my wife and I had saved huge chunks of our pay (100k+ in the bank), in addition to the fact that the businesses were already running at half-steam meant that the transition was stress-free and seamless.
You can make good money selling your time, but maybe it's not about money for them? By all other measures this game was a great personal success. At this point the dev is competent and successfully releasing games, they just haven't been commercially successful. Now would be a terrible time to give up.
My advice would be to run out of options first, then go work at that "elsewhere". Once you get settled into a career it can be really hard to step back out into solo dev.