What would happen if a cell did not have mitochondrial

Cells that have no mitochondria are unable to convert oxygen into energy, found in the form of adenosine triphosphate (ATP). All multicellular eukaryotic organisms, including plants and animals, have mitochondria in some cells, but prokaryotes and some single-cell eukaryotes do not have mitochondria.

"The mitochondria is the powerhouse of the cell"
Besides being a meme, it essentially describes what it does.  It produces energy for the cell, and the body as a whole.  In the mitochondria, the process of cellular resipiration occurs, which turns glucose into energy usable by the body.

Hope this helps!