Here's what should have happened:
As soon as the OP started being Managements Angel, his route should have been put up for bid. The next senior guy who last bid on the route was screwed by someone who bid it, and then did cover.
ALSO, any brother who would not help management in this way was now an a/h with a target on his back, thanks to the OP. I'm sure there's more than a few who refer to him as "da boy".
I hate stories like these, they usually come from centers with a weak steward. A good steward would have stopped this from day one, or at least got that route assigned to the next senior man who should have gotten it.
I imagine both the company and the union are laughing at the grievance. How was it worded? "I voluntarily left my route, and now I feel screwed"?? You can't be grieving that they didn't put you on your route, because they did. So I do understand why it's being ignored.
Hopefully you'll get it back after Peak, and this will be a lesson learned.