https://github.com/stenzek/duckstation/blob/master/LICENSE
Fast PlayStation 1 emulator for x86-64/AArch32/AArch64/RV64 - stenzek/duckstation
No matter what the author did to the main repo, the various forks will have the entire git history. From most recent forks git history you simply check out the most recent revision before the license change.
This is the commit where the license changed:
https://github.com/stenzek/duckstation/commit/9ca6b5430fb358b39f21ce0b2fc0268de954dd23
The parent link on that page takes you to the most recent before the license change:
https://github.com/stenzek/duckstation/commit/25bc8a64803df7e702db66e0f11d7b7d0fdc99f2
Anyone can fork the repo and continue working from 25bc8a6