I have to agree with the previous comments about not letting this situation overwhelm you.
Had the rat not died you would have used your TT as normal as ever. Now you have discovered something that you will have to eventually address. Whether you do it immediately, a month from now, or after you have had time to evaluated a number of approaches and decided which ones you like.
Our TT was three years old when we bought it and in the past four years and 30,000 miles I have discovered a number of oddities. These require some additional bracing and sealing between trip. But nothing that reduced the structural integrity.
The point is, unless the problem affect the road worthiness of the TT. Their is little difference between a hole punched through the wall by a foreign object or a hole caused by water damage. And, there is no reason you should not be able to enjoy you TT.
We bought our TT because it was the right floor plan at the right price. I would be hard to match those two again.
Good luck