Whether you had a hand in ending the mouse's life, or the mouse happened to die of natural causes is irrelevant. If you didn't dispose of the carcass or you can't find it (or worse can't get to it), the decomposition of that dead rodent is going to make your life miserable. That being said, I'm going to throw at you a few tips for taking care of this awful smell.
Now if you're simply trying to avoid the dead mouse smell, there are steps you can take. Don't kill the mouse (just kidding). My best piece of advice is do not use poison. When you use poison, you give up control ... control of where the mouse dies. If that little mouse eats the poison and wanders back to his nest, which happens to be inside of your wall, and then dies.... then you're going to have a dead mouse in your wall. At that point you have two options, deal with it or break down your wall and hope you find it. It's not the place you want to be in.
I'm guessing if you're reading this, the mouse is already dead and you trying to get rid of the smell... am I right? First of all, find the source of the smell and eliminate it. The saying "Follow your nose!" comes to mind. If you can track where the smell is getting stronger, you're probably getting closer. Find the body and properly dispose of it (make sure you use gloves and sanitize the area thoroughly). If you can't locate it, or if you can't get to it, then you need to bring in the big guns.
All the potpourri in the world is not going to save you from the hideous stench you're experiencing. All that's going to do is leave you with a horrible stench mixed with flowers. You're going to give yourself a headache, so stop trying to mask the smell. It's not going to work. Burn a candle? Don't waste your time... you need something that works to eliminate the odor, NOT mask it.
I always recommend Fresh Wave Continuous Release Odor Neutralizing Gel. The only reason I'm telling you about this product is because people say that it works. You have a problem, and I'm trying to point you in the right direction...