Will items dropped on the ground ever disappear?

Eventually yes, it will disappear. Every once in a while a city resets. A (usually, and it worked for me) way to do this is to make a new character and then load the old one. This will cause the entire world loot to reset so if you have some bodies laying around they will disappear and if you have stored some things in an unsafe location it too will probably disappear.

Throw the items that you don't want in a spot that you know you wont go.

Cell reset is affected by visiting it, so if they are somewhere you often pass trough, they may never disappear. So letting them laying in a city where you have a house is counter-productive.

Yes they do disappear after a while. I would suggest buying a house and storing your items in chests or storage spaces.