Why the earth orbits the sun from X to -X and not the opposite I wonder all the time, why the earth orbits the sun as expected from east to west(X to -X) ?
It could be different, for example from the west towards the east .
What would happen if that were the case?
The thing that keeps the Earth from falling into the Sun is that it orbits the Sun, once a year. We usually don't say that the Sun orbits the Earth.
Orbits have a direction or sense in space. What that direction is called is an issue of history and linguistics,
The Earth rotates around its own axis, this rotation also has a sense, and the same caveats about what this is called apply.
It is the daily rotation of the Earth around its axis and the tilt between this axis and the axis of the Earth's orbit around the Sun that determines for a given spot on the Earth where along the horizon the Sun will rise and set.
If nothing else changed except the Sun suddenly started rising where it normally sets, and setting where it normally rose, that would mean that the Earth started to rotate in the opposite direction around its axis.
We would call that retrograde rotation and it would be a surprise.
It's generally believed that the sense of rotation of most (but not all) planets around their axes is similar to the rotations of the planets around the Sun is evidence of the rotation of all the matter that formed the Sun and the solar system. The Moon also rotates with the same sense around the Earth and the Sun rotates with the same sense around its own axis.

What would happen if that were the case?

This is a great question and is hard to answer. It depends a great deal upon if the Moon was also now in the opposite sense or not.
But I can say one thing that would happen is that people would wonder why the Earth was rotating in the opposite sense of most other things in the solar system!