Once they enter the two-way rifle range, it'll be over. 99% of them will flee and never try it again. Only the hardened criminals in their ranks will stay to fight, but gang members typically suck at shooting, and have zero knowledge of even the most basic of tactics, so they'll be mopped up real quick.
I don't think I've ever not vomited when sick, courtesy of all the damn nasal drainage. It's always the same. Feel tired and overly hungry, post nasal drip begins, feel tired, vomit on night two or three, get all the other symptoms, then just deal with it until it fucks off.