So, the summation of ideas in this thread, in no particular order, is:
1. report him for harassment and blackmail
2. place him on ignore
3. go punch him in the junk if he's known IRL
4. continue to bot
5. lay low if the entire guild is being threatened to be brought into the scuffle
I can say, after being PM'd and called out for botting, to follow these ideas as they actually work. Well, all but the junk-punch, because none of my reports were made by IRL friends or known people. So, take some of the advice with a grain of salt and do what feels safe to you. If you feel laying low is best, then do so. My two bits were added just to show that it's still somewhat safe.