CAN Bus has its own voltage operational limits but is in general a very robust protocol.
What I believe happened to the OP's car is that this ground cable was causing noise in the can bus causing all the systems to fail one by one. But this by itself doesn't explain all of the problems he has had. I believe the ECM has a very strict check list and if it finds one error that COULD be related with other subsystems it starts shutting them down and doesn't let the car start.
They must do something about that.
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