Why can't The Dwarf leave the flask? The Dwarf in the Flask, of Fullmetal Alchemist: Brotherhood, is seen trapped within a flask during his first appearance.

At one point in the series, The Dwarf states that his greatest wish is to leave the flask (from FMA Wikia):


   Being a homunculus with no form, the Dwarf in the Flask was unable to perform any alchemy of his own. Furthermore, though the flask was the only thing that keeps him alive, [The Dwarf] desired to exist outside it.


However, due to the emboldened part above, it appears the flask is somehow keeping him alive (though he is only corked inside it). How does it do this, and how would he die if he left?
Because he had no form on his own. He's basically an essence of God, created from Hoenheim's blood.

If his flask would somehow break, his being would dissipate into the space, and lose his form and living consciousness.

Think of it as a soul with no body. Stuffed inside of a container, if that container would break, the soul wouldn't have anywhere to reside, and leave the world. (Al is a slightly different case, his soul is bound to the seal on the back of his neck).