Well, my reasoning for Casca still going to Griffith is basically that I have yet to see her character behave rationally when it comes to Griffith. Granted, we have yet to be shown explicitly how she feels about Griffith post trauma--she may not even know herself, just coming out of a brain...
I do not think that Casca and Guts can have a happy relationship at this point. First of all, Guts's character is the embodiment of conflict. Griffith noted this when he first met him--Guts fights as if to justify his own existence. The Struggler has no identity if there is nothing to struggle...