Are dt's ever fatal during alcohol withdrawal, and if yes, how do they cause death?

Yes. Delirium tremens are extremely dangerous and carries a 35% mortality, untreated (5-15% treated). The physiologic mechanism of death is a combination of neurologic and cardiac processes related to the unregulated hyper-metabolic state of dts. Neuro-cellular damage due to the chronic exposure to alcohol leads to cardiac arrest and death.
Yes. Alcohol withdrawal occurs when you have been drinking more than a few drinks on a regular basis for about a week or more and then try to stop suddenly. The body reacts to the absence of alcohol. Dt's or delirium tremens starts to occur 2-3 days into withdrawal. Death could be related to seizures, dehydration, or any number of other consequences.