[pushkins]

Firstly as a male I must stand up for my fellow man (chanting "burn the jock strap"....or something like that...lol).
But he is right....unless you want to tear out the walls in a search of the dead rodent (never a great idea) there is little you can do. The smell will in a few days or a weekish time frame go away. The smaller the deceased the faster it goes away. Now if you had a raccoon in there...you'd know it !!!!

A fully grown mouse can get into a hole as big as you little finger nail, they can climb up PVC pipe so they may well be coming from below not above.

Your best bet for the next week is to get one of those little air fresheners you plug in and don't worry too much about the health issues as long as the grandkids don't eat it there there is little danger.