Stealing Karka and Avadim

The Raavad in Hilchos Gezailah 9:1 seems to hold that there is a difference between stealing land and stealing avadim (slaves). By stealing land if the land is later swept away by a river it is no longer considered "b'ein" (it is no longer in existence). The thief is then completely patur from returning the land because of a general rule that "karka eina nigzeles" (land cannot halachically be stolen). The idea is that even though when you steal something you are chayav in onsin, this is not the case when you steal land.

In general, avadim are compared to land. Yet, the Raavad says that by avadim, if after they are stolen they die, you do have to pay. The question is, isn't there also a rule of avadim not being nigzeles.

Rav Chaim answers that while it is true that there are no kinyanei gezailah by either avadim or karka they are still not identical. This is because by karka, not only is there no kinyanei gezailah, there is also no maaseh gezailah. It's not only that land cannot halachically be stolen, it cannot physically be stolen either. By avadim, on the other hand, although there is no kinyanei gezailah, there does exist a maaseh gezailah.

Rav Chaim explains that there are 2 chiyuvei tashlumin a gazlan can incur. The gemara says that if a shinui happens to the object that gazlan must pay. In order to be chayav in this payment there must be kinyanei gezailah. However, there is another chiyuv of tashlumin if the item stolen is no longer b'ein. This chiyuv can be generated even with a maaseh gezailah alone.