One option is to get the battery repaired with a normal cell-pack and BMS, then dismantle the motor and remove the controller, wire in a normal motor cable and run with an external controller. If it's like other Bionx motors, I'm pretty sure it splits down the middle, so needs to be de-spoked to get it apart. That's a lot of work, but means the battery will be repairable in the future. It also gives a lot more options for power and speed. It will be legal with whatever power you want as long as you keep the speed cut-off to 15.5 mph.