Oh no.....I have just been through this myself. In my case my Stripes was a feral cat who I'd been able to socialize somewhat but not enough to make him into a house cat. We found him probably very soon after it happened, just a bit down the road from our house.
Our other cats are 100% indoors, for this reason - but Stripes would have been miserable inside even if I'd been able to get him through the door. It is awful. I'm so sorry that Mouse is gone. She is a beautiful girl! My worst day ever was last Wednesday, and every day since has felt terrible as well. Of course I've had animals die before, but at home, or at the vet's. This was especially traumatic. I wish I could tell you something, anything, to make you feel better, but I'm not coping either. I just feel like it was all my fault. To make things worse just a month ago my favorite rooster, Cocoa, was killed by a possum who managed to make its way into a run we thought was predator-proof. They were in that run for several years with no problems but after the tragedy I redid the run and found weak spots that had developed where a possum could have entered. I thought I was doing everything right, but clearly I wasn't. So I've had a month of near-constant crying. One thing you could try with Badger is cat-proof fencing - here it's called Purrfect Fence, and they cannot climb it. It wouldn't have worked with my guy, only driven him frantic. But that way Badger could have some outdoor time without the dangers of the road.
"Some of you say, "Joy is greater than sorrow" and others say, "Nay, sorrow is the greater." But I say unto you, they are inseparable. Together they come, and when one sits alone with you at your board, remember that the other is asleep upon your bed." Khalil Gibran