My Angry Birds app button is missing. The only way I can find it is through the market and it shows it as being installed. So I can open it that way.
from an empty spot on any home screen click the menu button and select shortcut and hopefully angry birds will be in the list. if it is you should be able to add it to the home screen. If not then you may have to uninstall the game and then reinstall to get the icon back. hopefully your not too far as far as levels go. good luck.
I was able to put it on one of the home screen, but it still does not show up on the screen with all of my apps.