I would imagine the frame (bottom part that the axle attaches to, not the walls and roof) are perfectly fine, the walls took the impact.
How much is it worth new?
Agree, in dealing with ins companies too I find that they are very quick to settle on property damage. For them the cost of a vehicle is nothing compared to the cost of medical. Vehicles are easy, medical is a nightmare. I bet you get a nice check for your efforts, not what you paid but close enough.
What is the wall frame made of, wood, steel, aluminum?
Depends what buy-back price is. Most of the components and appliances are probably fine if all that happened is to lay on its side. They have value.
The trailer can be fixed. It can be fixed back perfect, or fixed to not leak or be a danger and to be towable and useable. It can be fixed for a hunter's special (to park it in the woods and never move it again).
That you are asking means you have not done this, so I advise DO NOT try. Walk away.
The WD hitch probably would have damaged your truck more, so good that you had it off. It would not keep trailer from flipping in a dangerously fast turn.
If you enter an intersection under green or yellow then the intersection is YOURS! It does not matter if it turns red AFTER you enter the intersection. The law states "do not enter intersection under RED". Other drivers HAVE to wait for you to exit the intersection before moving through. No need to tear through and crash just because you saw yellow or red after the fact.