If the spring is broken its usually just the tab end of the coil that locks into the spool or the housing. I took mine apart, carefully and rebent a new end on the coil spring, slipped it back into its housing and then retensioned the starter spring. If the rope broke you should be able to find a suitable cord. Honestly it was just like replacing the cord or spring in a weed wacker, lawnmower, or chainsaw.
Mine has been working for over a year since I fixed it.
The only people who truly know where the edge lies, are those who have gone over.