Posted: 05/05/2013 at 17:00
Mint doesn't mind being rootbound. Mine's been in the same average-sized pot for years. You can also cut it back pretty heavily on top too. Providing it's got decent growing conditions it will come surging back.
The little flies won't hurt the plant outside. What colour are they? White? If so, there's little you can do to get rid of them apart from swipe at them with your hand. They don't do a lot of damage unless in plague proportions.
The benefits of putting the plant outside in plenty of light far outweigh the little flies.