I'm not sure if the fade-out behaviour directly links into the opacity of the object - but you can try doing a comparison with the opacity for your collision.
If opactity = 100
Object collides with object
--- Do stuff
If that doesn't work, you may be better off not using the fade behaviour, and coding a simple one yourself just be setting opacity of the object until it's at 0 - then destroying it if opacity is 0 or less.