What consequences should Gary face?
Firstly, he would be involved on murder. That's not a great experience to have, for most people.
He would at least be on trial. I don't exactly know how incitement to murder is treated in the US.
It could even be considered domestic terrorism (an assassination made to intimidate a group based on an ideological agenda/government policy). Then, I don't know what would happen, exactly. The FBI would probably get involved?
That's very clear!
In no way is "die slow motherfucker" incitement to murder, whether or not the person is question is actually murdered.