What would happen if time stopped ?
Time can't stop as such, but strong enough gravity can stop time.
Isaac Newton saw time as a linear flow from the past to the future. He saw time as an independent variable which is independent from space. This model fuelled many science fiction stories about time travel and time stopping.
Relativity changed all that. Time is actually the fourth dimension of four dimensional space time. When you travel somewhere you move between two points in space time which have different time coordinates.
In fact you are always travelling in the time dimension at the speed of light!
Gravity is caused by mass and energy causing space time to curve. Time passes more slowly in a gravitational field. At the extreme, which is a black hole, gravity is so strong that time stops.
A photon of light has zero mass and travels at the speed of light. This means that it does not experience time. Time is stopped for a photon.