First, the machine origin is top right rear where the switches are, so everything is relative to that.
If the Y-axis belts aren’t evenly tensioned then what will happen is the side with the belt with less tension will not move as much as the other side which has more tension — but it will pull on the belt so as to increase the tension on the end the motor is moving towards, then it will have to overcome the mechanical structure of the gantry, warping that before it will get out of position — in practice, uneven Y-axis belt tension increases backlash, but doesn’t usually cause other problems.
A bent axle on a pulley will constantly increase/decrease belt tension by a tiny amount, but won’t otherwise be an issue — until it breaks, which usually happens in short order (the shafts are quite hard and tend to break rather than bend).
See: