I agree with your major points, but depression is far from trivial. People sometimes refer to feeling a bit down as depression, but in medical terminology depression is specifically a disorder which has severe impact on your life, as well as being one of the main causes of suicide. As such it will be a factor in evolution, both as a cause of death and a cause of failure to reproduce.
The inverse of via negativa is that when the for potential death is there, interventions should be used without hesitation.
Insofar as death removing someone from the gene pool, again this is exactly the reason I bring up the gay uncle hypothesis. The idea being that the reproduction problems of gene for an individual may be outweighed by the reproductive benefits of the genetic family.
The other idea is that it may be caused by a common error like genetic disease.
