Vsauce explains, once again, why we should thank gravity. If you would us a straw that can reach the space and put one end of it in the ocean you wouldn’t lose the water form the oceans. That is simply because gravity would hold that water down.
In any case, that water would still go up for about 30 feet because of the pressure the fluids exert on the layers of fluid (water, air) that are above them. A balloon flies to the sky because the pressure of the air below the balloon is greater than the pressure above the balloon.
The same principle is applied in the cosmic straw too. Michael also explains why Earth loses a good amount of Hidrogen each year and why we should not fear. As always, his videos shed light on things we did not knew existed, like strange questions.