Here's another variation on that idea.
Say there's a cart/wagon thing that can carry 6 players to safety. There are 3 jailbreakers armed with some rudimentary equipment, and some prisoners in cells, and guards which spawn dotted around the map but mainly at the jail and at the wagon thingy. Some guards spawn near a stable and can ride the horses.
The jailbreakers then proceed to the cells where they shoot the locks (perhaps like breaking a door in Native? Though it's got to be immune versus fists and kicks..) after killing the guards. The prisoners can grab a few weapons from a small arsenal in the prison and off the guards. They then proceed as they can, to the wagon as quickly as possible. The guards try to stop them. If the prisoners do get on the cart and prepare to go away, via some plotted route, the guards can try and blow the prisoners up with the dynamite, which will stop the cart.
Meanwhile, there's a timer ticking in favour of the guards.