Taillight is only sold as a complete assembly. If I were you I'd search for a used one at a salvage yard - you can search salvage parts online, and many yards will ship the part to you. Will be about half the cost of a new one.
It's possible to remove that lense, so it would be physically possible to replace it. The only issue is that you can't buy that lense separately from anywhere so you're stuck finding a whole taillight assembly.
I'm thinking it could have been more expensive 1/2" to the left. A painting accident would have been worse and then needing to deal with the color change of a blue metallic. This probably worked out in your favor with the taillight taking the hit.
I think the hit to the paint wouldn't have done anything.. It really didn't even hit the tail light that hard I was surprised to see the damage it did do.
