That is going to require some serious Madness protection on your part. I've had two opponents try this on me and I make a B-line for the Madness every time. Also, Self Loathing isn't particularly effective against him since he ignores his own weak damage and reduces his moderate to two. If you can guarantee a severe then that might be worth it (unless you've tricked him or allowed him to cast Charge Up! first and he's at 3/5/6).
As a mainly Freikorps player I have to say there's nothing more annoying than Tarpitting my SAS, especially with a bunch of puny models ("chump blocked")! He doesn't have a particularly effective method of getting himself out of melee other than killing whatever has engaged him. His gun is magical but his fists aren't so small fast moving spirits are great for tying him up - this has been a problem against Night Terrors and Kirai's crew. In doing this though remember the goal isn't to kill the SAS but rather to tie him up.
My SAS has died in exactly 1 game since the start of the year, and that's because I put Frame for Murder on him. So the above posts are correct, don't try and flat out kill him unless you have a high damage model with the RJ in hand to cheat. If he's in a non-freikorps crew or if you can somehow kill the Libby then he's a lot easier to take down; but taking down libby is usually harder than taking down SAS unless you can make her a mannequin.