And then the cat's going to think "wow they demolished an entire wall just to get my present. I've got to get them more of those!"

Coming from someone who has owned a lot of mice (they repopulate like crazy) they're small and really don't have much of a smell as they die. If anything just light a candle in that room, but you probably won't notice an odor anyways.

Don't sweat it. Seal it up.

Close the hole it got in and you have no problem. You'll never smell it anyways. There has been a dead mouse in my mother's basement for over a year now and we still haven't smelled it

I believe you can fix this problem with the bigger animal theory

do it ASAP I had this happen to a friend and omg it smells especially if you're in a warm state bleh good luck lol

As many others have said, you won't smell it. Mice don't really smell. We had a mouse problem at my last job, I stumbled upon a few dead mice in my time there but it was never because of the smell drawing my attention to them. Never smelled them, nobody else ever did, they don't smell much if at all.

You could also blow hot air in the wall, making it so hot the mouse dries up instead of rotting away.

Or you just cut a tiny hole. Or better yet, slip packets of desiccant into the crack. They'll mummify it and it won't smell at all. Duhhhhh

Living mice are stinkier than dead mice. Don't worry about it.