Not Cabelas, but I have had Sportsmans Guide backorder an item (not ammo) and finally cancel the order.
Original order was to be a Christmas gift. When it was backordered, we bought it locally to have it in time for Christmas, but I decided to play out the backorder process and see where it went. Every month for the next eleven months they sent me a card, extending the backorder another month and offering me the option to cancel. I just kept extending. Meanwhile, the exact same jacket was showing up in their catalogs, under different names and with different stock numbers, but always at the same price. They could have sent me any of those ... but they didn't.
Finally, after they couldn't trick me into cancelling ... they cancelled.
I don't trust any of the big sellers, regardless of how good their reputation seems to be (even Cabelas).