[Cory]

Hard to tell much from those pics. A big one is seeing the ways to see if the original scraping pattern is there or if it's worn down.

The thing he had to grab is called the drawbar. It's just a really really long 7/16-20 bolt. Any mill without a power drawbar is going to have one and you'll need to use a wrench on it to tighten/loosen the collet. The keyway does nothing in terms of clamping the tool. The only purpose it serves is to keep the collet from spinning while you tighten the drawbar. All the clamping force comes from the interaction of the taper on your tool and the mating taper in the spindle.

There is normally a pin inserted in a cross hole in the spindle that matches up with the keyway on the toolholder. It's super common for these to snap off. You can use it just fine without the pin in there, or you can replace it. If you don't replace it you should at least make sure the remains of the snapped off pin are removed so that it doesn't gouge your toolholders.