The smell from small mice in my walls has lasted up to 3 to 4 weeks. We had wainscoting on the hall wall so I accessed the area the last time and found the skeletal remains of 4 or 5 small mice which had happened over thirty years. They come down from the attic and can't get back up and die. I think I've plugged the hole since it's been over a year. If you have sheet rock, you'll just have to wait it out. The bathroom was affected the most so we just kept that door open to let the smell out. You can't really cover up that dead smell.