NYCone: electrolysis should eventually remove the rust between the slide and the static jaw. Have patience. If it does not free up, the slide can be removed from the static, but it will take a bit of work.
First do NOT hammer on any part of the vise. The holes in the slide were caused by some gorrilla using the precise, machined slide as a convenient anvil.. any hammering may cause the slide to finish cracking off and then the vise is nearly worthless, or at the very least, a much bigger challenge..
To get the dynamic jaw to come out of the static, I'd use wedges. Cut some wood pieces, like pieces of 1"x3" or whatever will work. You need to have two pieces that fit into the inside curve of the jaw supports, above the slide. Sand or shape two pieces to be 1/2 round and fit snug against the inside of the jaw opening. In the gap between the two pieces of wood, you are going to drive wedge shaped pieces of either wood, or metal or maybe plastic. There are various types of wedges available at lumberyards. These are used to shim up houses, or beams or in smaller instances shim a door or cabinet. You want to find something that you can drive into the gap between your jaws/wood blocks.
Even a hatchet/ small axe head has about the right wedge shape.. You are essentially making a manual 'jaws-of-life' to pry open the jaws..
With the appropriate wood blocks and wedges in place, drive the wedges in, and watch the area of the slide where it comes out of the dynamic. Mark the slide with a sharpie or similar to be able to see any movement as the slide finally moves..
IF you have not been able to get the mainscrew removed, you must unscrew the mainscrew as the dynamic jaw is forced out of the dynamic.. If you were able to get the mainscrew out, then you just need to keep driving in the wedges, and eventually the jaws will move apart..
If the dynamic and static just don't want to separate, use heat on the vise static. A propane torch, or a good electric hot air gun will raise the temperature of the static jaw to several hundred degrees, this will slightly expand the iron. Hopefully getting the rust to let go it's hold.
Sometimes the wedges and heating process have to be done for days on end before the dynamic inevitably does succumb to the pressures and starts to move..
Soaking the slight gap between the dynamic and static with your favorite pennetrating oil may help.
I'd likely try some CLR bathroom rust remover, or in extreme instances some Muriatic Acid, [home depot, pool chemicals section]. IF using acid, it must be outdoors and use all the proper protections and have baking soda mixed in water to pour on any spills or clothes to neutralize the acid.. BE CAREFUL. and don't breath the fumes..
The dynamic and static WILL come apart.. You just have to convince them to do so.
PierceA