What caused the damage? Any of a number of things. Spokes that are too tight can cause pull through. But spokes that are too loose can also cause cracking and pull through. Too tight is mostly self explanatory. If the spoke is too loose, the spoke goes through a loosening and tightening cycle that works aluminum. Aluminum doesn’t work very well and will eventually crack. Think a pop can that you flatten and bend back and forth repeatedly or a piece of aluminum foil you try to straighten out. Further down on the list is impact although that is way further down on the list and is somewhat related to the loosening/tightening cycle.

How much life left? None. Zilch. Zero. Bupkis. Get some butter and marmalade because it is toast.

Will a double wall make a difference? That is a double wall rim. A better quality double wall rim and, perhaps, double butted (or triple butted) spokes will make a difference, although 12,000 miles isn’t too bad for generic wheels.