If no Bitcoin is being minted and a certain amount is lost every year to burn addresses or mistakes, it stands to reason that at some point the amount Bitcoin in circulation would approach zero. A hacker group could grind the economy to a halt by gaining control of people's wallets and burning money, creating much larger deflation than what is caused by the economy growing.

On the other hand, as far as I understand there is a huge number of inactive coins that no-one knows whether they've been lost or not. If those coins start moving it would effectively create a large inflationary pressure.