I can guarantee, from personal experience, that they will. Deposits in a nice dry rock shelter will preserve the best. Rest assured that you will provide valuable data for future archaeologists. I often said that if fire consumed our building, which housed the results of four seasons of digging in a large southwestern prehistoric pueblo, that if I could save just one kind of artifact, I would grab the ten or so boxes of exquisitely preserved prehistoric poo ( several hundred samples roughly 800 years old) that we had retrieved. All kinds of good information on diet, disease, DNA, blood types - don't get me started......

And then we could talk about historic outhouses. All kinds of things occur there aside from the usual material. Just don't excavate them before their time.