That's what I believe will happen... China's already loosening the border between itself and Russia, and most of the Eastern edge of Siberia has more in common culturally, ethnically, and economically with China than Russia.
One day Putin or Medvedev will wake to the news that 500,000 Chinese troops sit 300 km inside Siberia, which is now annexed because it is "traditionally more Chinese than Russian".
Russia does not have the men or materiel to stop it, nor the need or ability to harvest the natural resources of Siberia. China has the men, the materiel, the need, and the ability.
Well, unless global warming does indeed arrive, most of Siberia is not worth much. Mining and forestry, and a good place for a gulag.