Whole reimplementations have survived. IBM BIOS was the only original BIOS for PCs. Phoenix Technologies had a team read the source code for IBM BIOS (it was published in the user manual for troubleshooting) and wrote a specification for it which a different team wrote software from, making IBM compatible machines possible

I don’t know what law an emulator could be killed under, unless a license holder breached the user license as part of the development