Do embalmed people still decompose?

I have recently returned from California and whilst there I visited forest lawn cemetery. I went in to the great mausoleum to see Jean Harlows' tomb aswell as a good many others. I know this may seem very morbid but can anyone tell me if these embalmed stars stay intact or do they rot away and how does the cemetery deal with this as I read somewhere that tombs can spill body fluid if they are not sealed properly.....Any answers would be appreciated......I am quite serious in my request so please answer me seriuosly.....very many thanks.