You know (x, y) of the object, you also know the (width, height). You know xMin, which is left of your screen, and xMax`, which is right of your screen. If at any time either of these two conditions happens, it is not coming back:

1. (x + width/2) < xMin
2. (x - width/2) > xMax

Otherwise it is still within xMin and xMax, it will come down in the visible area.

You might need some other solution if the objects are not uniform scale, but this should give you the basic idea.

You know (x, y) of the object, you also know the (width, height). You know xMin, which is left of your screen, and xMax, which is right of your screen. If at any time either of these two conditions happens, it is not coming back:

1. (x + width/2) < xMin
2. (x - width/2) > xMax

Otherwise it is still within xMin and xMax, it will come down in the visible area.

You might need some other solution if the objects are not uniform scale, but this should give you the basic idea.