I agree, insurance should cover this.
I'll tell you a funny story from a few years back.
A buddy of mine was driving his mk4 and broke the inner CV on the driver side axle.
It swung around and busted a huge chunk out of the case and he lost all the fluid.
The repair was simple. Drain the fluid let it drop dry. Clean all the oil from the area using brake clean, and use JB quick steel to patch the hole. In his case, the hole was too big so he had to smear the jb weld onto a piece of cardboard and put in over the hole like a patch. The transmission worked great for years like that. Also, any skilled aluminum welder should be able to fix that, but you could run into heat issues as mentioned above.