how long to get a response?

At least 48 hours if you didn't bump. Longer if you did since your ticket is now at the end of the queue.

Had the same - took about a day to get a response saying they'll look into it; 2 days later he's still playing though so dunno if it takes a while to ban someone or if telling people in detail how they should kill themselves and why it's important that they do doesn't violate Riot's standards of behaviour... either that or since the account is obviously a bought lvl 30 account already they figure it's not worth banning? Dunno.

I would not hold my breath while you wait for the player to be punished. I had similar case ten days ago (homophobic slurs are supposed to result in instant suspensions), I reported via the report system and a support ticket (provided screen capture), the ticket has been closed and the player in question is still playing, so he wasn't "insta banned" like people say IFS works. IFS (and even support) aren't working properly. Some griefers occasionally get punished, but most likely that is only a small percentage of them. Therefore you can only hope that the reports/tickets you create hit the guilty. Oh, and keep on breathing. Breathing is the important part!