1. Parts of the map will be missing and inaccessible. They will be the same color as the background, and my character will be unable to travel into them. They are perfectly rectangular edges, too, so it's obvious that it's a part of the game that isn't loaded.
2. Characters will get stuck performing an action, like casting a spell.
3. Actions will be un-performable. The outlines of objects will light up, as if they could be interacted with, but clicking on them does nothing. Similarly, I will click items in my inventory, but won't be able to sell them/swap them out/etc.