Hey, am sure it is fairly common practice to fill a site if someone leaves. Some may get their money back, some a credit and some nothing. I think the "nothing" - although not right - is the most common by quite a margin.
We did get our money back in one case we had to leave early - Steamboat Springs, CO. Our neighbors were seriously violating rules even to the point of setting up a tent on OUR space - even though tents were not allowed in the RV section. Said they did that as there was more room on our site. We said we were leaving and manager said no refund; the asst manager (who was to become the manager in about a month) freely gave us our money back for our upcoming paid for nights when the manager left the room....she had overheard the whole thing. We had not even approached her on this; did it of her own accord.
Just depends how you want people to remember your place and who and how you tell about it....if they care, that is.