Floyd
I presume you are referring to cold conditioning, or lagering, as opposed to secondary fermentation (which is different. In secondary fermentation, active fermentation is still occuring, and there is unfermented sugars available for the yeast.)
For a single stage fermentation that is then racked to another vessel for cold conditioning, all the dead yeast is left behind in primary. So what you have is live yeast in suspension. That is then chilled, causing the yeast to flocculate out, and drop to the bottom. It is the cold that causes the yeast to drop, not the fact that the yeast has died. So it is still live, viable yeast (granted, there will be a certain amount of dead matter come through in there, but that will be minimal). Also, due to the cold, that yeast will be (relatively) innactive. Autolysis (the yeast consuming itself) is less likely to occur in these cold conditions.
For those that have done a short period secondary fermentation (ie racking prior to the conclusion of primary fermentation, and allowing fermentation to continue in the secondary vessel), a determination is made as to whether or not it is necessary to rack a second time into a clean vessel for cold conditioning, and in a practical sense, this is rarely done. It mainly comes down to how much dead yeast has dropped in the secondary prior to chilling (which comes down to how long it is in secondary fermentation stage, and how much sugar was left for the yeast to consume). For the small amount from a 24-48hr secondary that drops out dead on the bottom, the contamination risk of the second transfer is (often considered) higher than the risk of leaving it on the (small amount) of trub. So it comes down to a numbers game.