I received an e-mail from a gentleman, asking what the artillery did if they were overrun if they were not armed with muskets. I responded directly but will also respond here, just FWIW.
The artillery in the Civil War (and AFAIK, just about every other war) depended primarily on the infantry for protection. It was a mutual support deal, as the artillery supported the infantry. If the infantry gave way, the red legs rode their horses or rode on the limbers to escape, or just plain ran. Abandoning the gun was a disgrace, but as many soldiers have said in one way or another, disgraced beats dead.
If the situation allowed, the gunners could hitch the gun to the limber using the prolonge, and continue firing in retreat. "Prolonge?", says you.
The prolonge was that rope you see in pictures wrapped around the hooks on the gun trail. If the gun was limbered up in the normal manner with its lunette (the ring on the end of the trail) over the limber pintle, the barrel was pointing downward and the gun was not usable. So the prolonge was hooked to the gun lunette and to the limber and the horses dragged the gun along the ground. That way it could be loaded and fired in a brief stop or even loaded while moving. I would imagine a pursuing cavalry unit would not like coming around a bend in the road to find a 12-pounder, double shotted with canister, waiting for them.