Seems to have worked well enough for OpenBSD, OpenOffice (and then LibreOffice from that), Jenkins, OpenSSH, Apache Server, WordPress, Inkscape, Webkit and Xorg.
When did Java get forked? The closest case I can think of is the Oracle/Google lawsuit, which 1. Oracle lost, and 2. wouldn't have even been a thing if Google had forked rather than reimplementing.
This drama has already damaged Rust and it needs to be addressed ASAP