You can see the fireworks from the balcony BUT it's not the best place to watch them. You really do need to see the castle. I would call the balcony seats a partially obstructed view of the fireworks.
You won't be able to get to Main Street in time to see the fireworks so the best thing to do is to watch it from the balcony and then see if you can get back another night to see them from the hub or from anywhere on Main Street.
In fact...this is what I did on another day (a few days after the dessert buffet). I watched the fireworks from the hub and then headed for the second performance of Fantasmic. Got a great location in front of the island (on the ground but still a great location) with no problems at all. So...good view of the fireworks and great view of Fantasmic. I was in Disney heaven!