Is the idea that a code base reset makes something stop being open source? Or that the number of people doing the reset matters?
I don't see why either of those would be true. The project isn't dead just because it's in a different language now, and for liveness purposes it doesn't matter how it got to that different language.
I think the point is that an “open source project” is more than just the code and license, it’s also the community that builds and maintains it.
A fast rewrite of Bun in Rust has effectively alienated most of the people in the Bun community, so in that sense the “open source project” has died. It’s no longer a community project, it’s just become a personal project again.