Today, in possibly the most unfortunate circumstances, the strap on my backpack snapped (new backpack)
Something very similar happened with my Samsonite backpack two years ago, mere weeks after I bought it. Luckily I reacted quickly and was able to grab it before it hit the floor.
I took it to the shop which sold it to me, and berated the bag. Three days later I got a call from Samsonite Europe and they groveled and sent me a 300 voucher for any Samsonite product.
In any case, I'd raise hell with the backpack manufacturer whatever you do, and make the insurance pay for repair/replacement. The rMBP is a premium machine, and although it might work without problem, you do not want that dent to affect the resell value.
RGDS,