The problem of what happens when the author is unable to keep working on the source code has come up a LOT in the .NET space. One author (of both books and OSS) has even written up [0] the pro-active steps he's taken for when "The Emnuggerance" (as Pratchett called it) takes his abilities.
[0] https://www.thereformedprogrammer.net/how-to-update-a-nuget-...