Regarding the evacuation itself, I'm not entirely sure that it's such a mortal danger on a lowish 737.
I've read an incident report of an RTO followed by evacuation in Ireland on a 737 where one lady broke her neck going down the slide and several others had very serious injuries. The main issue was people piling up at the bottom of the slide.
From this I assume the cargo fire extinguisher was fired and the fire light went out
Seeing as there is no heat detection, only particulate matter detection, and Halon levels are being kept above 5% for the first 60 minutes, would the light go out? I have had a cargo fire warning on the ground from a disinsection spray can being let off before a ferry flight.....would Halon be any different?