First the gang members need to get out of lockup. If it gets bad enough where guards leave their posts you can bet that there are going to be some dead inmates before they take off. No guards are NOT going to walk away wondering if he will ever going to bump into a bunch of guys that he left locked up during SHTF.
Next, allot of the animals will kill each other before they leave the prisons, Aryan vs Muslim, Black vs Hispanic, everyone vs everyone.
I honestly don’t think these gang bangers will be organized enough or have the wits to do much more than terrorize certain areas of cities. There won’t be any 100’s of inmates storming farmhouses. Maybe some small bands of raiders.
When shtf is starting out the military will prolly declare martial law and round up most of the inmates for hard Labour and execute the worst of the worst.