There are three main aspects to life: breath, energy (or food), and reproduction. Cells breathe or exchange gas, they consume energy, and they reproduce. Essentially if cells weren't alive, we wouldn't be alive. There are billions of cells in our bodies and they are constantly dying and recreating. If one cell in our body dies, it would not affect us. When we start dying, you know something is wrong and your cells are losing function. If your liver is failing, the cells that are specialized to create the liver or operate in the liver are malfunctioning which can cause a greater effect of overall death. So, to answer your question, we don't know if particular cells are dead or alive because there are so many but if you're healthy then your cells are alive and functioning correctly.