Why doesn't Artie just take a shit on the studio floor and then spit in Howard's face? He'd be making the same point.
Fuck this junkie. There's just no reason to keep him around. He's a mediocre talent. There are a lot of mediocre talents out there who could do his job, and more than a couple of really talented comics who would kill for his job and do it a whole lot better. I just don't get why they're keeping him around.
There's another reason to get rid of him. If he dies on Howard's watch, Howard's going to catch a whole lot of shit (and rightly so). If Howard fires him and something happens, its not Howard's problem, and he can say, "I did all I could". As long as the piece of shit is on the show, it will only end badly for all involved.
And then there's the school of thought that Artie's death and/or breakdown is exactly what Howard's waiting for, because he thinks it will make for great radio. If that's the case, then keep him.