If an Admin was compromised... The Server is Compromised. Remove the threat & lockdown the server (automatic with WICK or similar bot) / manual process:
LockDown Server
If the Server Owner account is compromised... the Server is lost. Attempt to change the password, but if ownership has been passed to a new account, then recovery is near impossible.
Discords are COMPROMISED, not hacked. Compromises can be avoided. Damage for all other unavoidable attack types can be mitigated. Study the fundamentals to prevent future attacks.