Plasma membrane is found in all cells and separates the interior of the cell from the outside. This membrane is selectively permeable, regulating the entry and exit of particles in and out of the cell. This ensures homeostasis, i.e., constant internal composition of the cell.
If this plasma membrane ruptures, homeostasis of the cell is disturbed, the constant composition of the cell is lost disrupting the normal functioning of the cell. The cellular contents present inside will leak out. If a cell has a damaged plasma membrane, it gets killed.