I am currently cleaning up my paper files, which lead to the archival and scanning of paper documents of many dead projects. So far, I archived completed ideas, or variant ideas of games I do not own anymore. They will be eventually be released on my Haunted Archives allowing you to notice my twisted mind.
But for video/board game projects, I have problem determining if a project is really dead since any idea could be reused or redesigned into something else. So an idea is never really obsolete. I though of criteria like discarding multiplayer game ideas, but again, multiplayer mechanics could be used in single or two player games.
I scanned my Neopet obelisk war idea due to the copyrighted theme and the multiplayer game, but again, some mechanics are reusable. I will be archiving my master of magic mod attempts for: Warlock, Elemental and Unciv video games. Again, many ideas in those files overlap with the many board games projects I have attempted over the years. So even if I do not wish to mod those games anymore, a lot of content from those files is far from being dead. You could argue that only a small percentage will be usable since it's more specific to the modded game's mechanics.
What are your though?
How do you determine that an uncompleted project is obsolete?