It is a terrible thing for a non black person to use the n word. (There are reasons why black it’s different when back people use it). The CONSTIUTION however allows people to say terrible terrible things and not face any punishment from a government actor ( which includes public colleges). That’s the bottom line.
And no the arrest of the idiot who made a death threat does not moot the issue. It’s a crime to make a death threat. It doesn’t matter if it’s for racist reasons or personal reasons unrelated to any racial or other issue. Of course people should report crimes. They should not be told to report things that aren’t crimes to the police. And a university shouldn’t say they will take disiplinary action against speech that isn’t a threat or other crime.