Open Source is one person

Has anyone seen any stats on what happens to a single maintainer project when said person is hit by a bus (or meets some other demise)? With that many data points, there should be enough of them by now to study it.

Is the project taken over by another, single developer? Is it replaced by a similar project? Does it just go away?

It depends. More common than getting hit by a bus is that the maintainer loses interest, or doesn't have the time to put into it anymore. When that happens I've seen all of the following happen:

* Someone forks the project, and eventually the fork replaces the original

* Another, possibly new, project that fills the same niche becomes more popular, and eventually replaces most usages of the first project.

* The original maintainer hands off maintenance to someone else.

* People keep using it, even though it is no longer maintained, and maybe make their own forks to fix issues they have, but none of the forks really catch on

One of the strengths of OSS is that if the developer disappears, or goes rogue, or changes the license terms, someone can fork the project and keep it going. With proprietary software, if the company (or individual) who makes it disappears, or decides to discontinue it, or change the terms to something unacceptable, you are just out of luck. Hopefully, you can find a competing product that meets your needs.