Usually if the rod turns with the nipple it will unscrew from the top. If that's not happening I would try to immobilize the rod while unscrewing the nipple.
It sounds as if you've been able to get at least a little space between the nipple and the glass. Use a pair of needle nose pliers to hold the rod and keep it from rotating while unscrewing the nipple.
I used a pair of 10" pipe grips used in reverse i.e opened outwards into the broken glass ring, I managed to turn the glass a little before it broke into 2 pieces. this took about 10 seconds to do.
Power was turned off and goggles worn.
First, this is probably a bad idea. Connecting the wires and then just reinstalling a non-working switch is not good practice and confusing to the next person.
A standard light switch has two wires going to it. When the switch is on, those two wires are internally connected, and when off, they are disconnected. So, to make it "always on", you ...
Assuming that the wiring is as you think it is, which you can verify by disconnecting one wire (red or black) at a time to see what the switch does, yes that is perfectly normal (provided the screw terminal can handle two wires, which may or may not be the case) and, yes, you can split.
Replace the single switch with a double like this one:
A double switch ...
each circuit should have it's own hot & neutral wire, the circuit you have drawn looks like they have used a common neutral wire for two separate circuits, (the lighting circuit and the outlet circuit). that's not a good idea and not allowed.
This is how it should be done. the first circuit should have a fuse to the switch: