What would happen if the moon did not exist?
If the Moon did not exist there would not be life on Earth as we know it.
The Moon is an important stabilising factor in the Earth's axis tilt. It keeps it in the range of about 22.5 to 24 degrees by its gravitational pull on the Earth's equatorial bulge.
The sun and other planets also pull on the Earth. If the Moon wasn't there the axial tilt would change wildly. Venus has flipped upside down as a result of the pull of the sun and other planets.
The worse case scenario would be if the tilt was close to 90° like Uranus. One hemisphere would have permanent Summer and one hemisphere would have permanent Winter.
In my opinion, even in the absence of Moon, there could have been evolution upon the Earth. We would be here to discuss questions like this.
More relevant for life to exist upon a planet are appropriate level of solar radiation and atmosphere with befitting mixture of gases like oxygen and nitrogen.
In the absence of Moon, we would miss everyday spring and neap tides in river mouths, estuaries and bays, with extremes on New and Full Moon days. Only sun-oriented tides at aphelion and perihelion would prevail.