This is not uncommon. I know of many other repositories serving a similar purpose that disappears from GitHub. Author probably got caught (e.g. leaking their email in a git commit). Many Chinese people have QQ email addresses which are linked directly to their real identity.
being one of the developers of the Clash core (https://github.com/Dreamacro/clash) and its closed-source (free of charge) premium version (clash-premium), i'm really heartbroken seeing this - everything is tearing down.
even without the context of being in China or Iran, Clash is still an awesome piece of software that can be used everywhere, with proper understanding of computer networking.
i ain't sure if both Dreamacro and Fndroid are physically safe now, but i'm sure they are both physically in mainland China.
This GUI for Clash by another author was also "removed" and archived (it seems the "main" branch is still there if you browse branches) https://github.com/zzzgydi/clash-verge
They won't face any jailtime (this is for sure), but they might get controlled (e.g. more surveillance, limited internet, cannot buy new devices, rigorous checking of their bank account, etc.).