Joanie

You might want to pull its little weed friends out... they will compete for nutrients in the soil.

Make sure that the pot has good drainage. I put some of mine in nicer pots last year, before I knew what could go wrong, and the poor drainage killed a maple. If the pot only has one drain hole, make sure it is covered with a fairly wide mesh and no rocks to block it. I would even consider drilling several drain holes around the sides of the pot, as close to the bottom as you can get. A layer of water just sits at the lowest level of the pot, because gravity is no longer enough to pull it down through the drainhole, and maples in particular are prone to root rot.

Cut off whatever is dead (you can tell by scratching under the bark, if you see green it is still alive) and give it lots of time. Time and patience are the hardest thing to get used to in bonsai. Trees take a long time to recover and grow, and your little maple has lots of potential if you give it plenty of time. Make sure not to stress it, because it will need its reserves going into winter.

Good luck!
Joanie