great

Qi yin and yang are never truly lost. they are the fundamental constructs of the cosmos. they just change form and change from one to another. during birth Qi is condensed int form and during death the physical body is no longer able to hold the qi in forma and is dissipated. even after death Qi is present and yin represents deacay and the physical is dissipated into the soil as minerals. what u take from the cosmos has to reach back to the cosmos and the is what happens with Qi, it is never truly lost. 

As per the source of yang during death. Death happens with extreme yin and  yin always has a seed of yang in it and Vice versa.