What would happen if the plasma membrane ruptures or breaks down?

If the plasma membrane ruptures or breaks down result in cell death.

Explanation

The main function of the plasma membrane is to protect the cell from its surrounding environment. The plasma membrane is composed of a phospholipid bilayer, which is two layers of phospholipids back-to-back.  If the plasma membrane ruptures or breaks down, the cell will not be able to exchange material from its surroundings by diffusion or osmosis because it acts as a mechanical barrier. Thereafter, the protoplasmic material will be disappeared, and the cell will die.