The life of a chain itself is a very open and subjective thing.
Run it hard, launch it, pop wheelies, drag racing can all wind up shortening the life or mileage you will get as compared to just riding around cruising with occasional throttle. ???
Agreed you need to try to find out why it snapped.
Agreed you should think about replacing sprockets as well cuz if the teeth are worn down a bit and you put a new chain on the new chain will in short order wear itself into the worn sprocket teeth possibly shortening the life of your new chain.