Cells die in two ways- apoptosis or necrosis.
Apoptosis is programmed cell death and, as the description says, it dies over a period of time and the cell is partially recycled. This tends to be planned and a result of unused or misplaced cells.
Necrosis is quicker, uglier and releases toxins which are not ideal for the brain. This happens more often with trauma.
There is also a large gray area in the middle where cells can die with properties of apoptosis and necrosis. Using microscopes it can be very difficult to tell which is happening.
However, in cases of blunt trauma, if certain cells (e.g.: neurons) die then the dead cells may be engulfed and/or replaced by other cells in the brain such as [micro]glia or astrocytes.
Good read: ( about neurones)
https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Life-and-Death-Neuron