Vacuum doesn't suck air, it is the other air which pushes it into the vacuum. Air like any other fluid will expand to fill the volume.

So you would expect the atmosphere to spread out to fill the rest of the universe - and without gravity holding it onto the Earth, it would do.

Vacuum doesn't suck air. In a vacuum it is the other air which pushes it into the empty space. Air like any other gas will expand to fill the volume.

So you would expect the atmosphere to spread out to fill the rest of the universe - and without gravity holding it onto the Earth, it would do.

Edit: Yes some air is continually lost. The molecules in the atmosphere are moving at a range of speeds, some of the very fastest ones will be moving fast enough to have enough energy to overcome gravity and escape. This is especially true for the lightest elements, eg. Helium, which move fast and feel the effect of gravity least.