Well, you know: if those feelings of guilt or whatnot contribute to the delaying of the development, maybe whichever Developer experiences them, should first get some Psychotherapy before getting back or deciding to not go back at all anymore and do something more "grass-touchy"
.
Because I know from my own, personal experience, that sitting in front of screen for too long without "touching grass" can be really dissociative for people with a bit of a "Hyperfocus"-problem, that prevents them from feeling their own physical and psychological needs during that process. It's common for several mental health issues and usually an indicator, that people need help.
So, I think I'm on the side of whomever wants to motivate them to get this very help and then either come back with a better "self-care" awareness, which would also result in better estimates of how long certain work will take without burning themselves out or to call it a day and communicate that they decided to explore other/different things in Life and maybe open up their Code to the public with the only "limiting" - because it would also be kind and respectful that way - caveat to have other Developers, who fork their projects keep the Credits/mentioning of them as the original developer and designer of the original idea in there.
That would feel and sound reasonable and respectful to both the developer and the people advancing their original idea and improving the Code and everything around it.
A simple "based on the Original Idea of Innoxia/Fek/whomever" in the Credits or even Intro Screens would be respectful and still allow others to build upon the hard work that these Devs did in the Future, i.m.h.o.
But to cling to these ideas and hinder others to build upon them, feels a bit off, too - because ideas obviously are meant to be shared and improved
together with others...if an idea isn't shared, it eventually
dies (off)...
So, yeah, I'd ask the Developers, how long they're planning to cling to their stuff before allowing others to build upon them as a foundation? - Because if they don't feel like or mentally/physically cannot keep it going anymore, the Code and idea is eventually gonna fade in the Annals of History anyway...
But if others are allowed to build upon it and mention the original Author of the idea behind their projects, I think they could live on for a very much longer time and even be cherished for it.
It's all about tact and respect again...and if people build upon their work with respect for it, I don't think there should be a problem. But, of course, the legal side of things ("property") might disagree as long as they do not declare it "Free Code" by themselves, where the pettiness kicks everything into the bucket...