Unclear, actually. Of course there'll be a move in the obvious direction after the decision, and it could affect stock price for months; that isn't important for people like me with long time horizons. But a total Myriad victory pretty much guarantees another round of legal challenges as soon as the strategy is worked out. Some sort of mixed decision (obvious one is saying that isolated DNA of the consensus sequence [maybe also un-isolated cDNA] is not an invention, but allowing everything else to be patented) would probably minimize ongoing legal expenses.
Myriad will lose ~20-30% percent of BRCA business if isolated DNA patents fall. They are trying to spin it and say their patents will be fine b/c they rely on primers and cDNA. However, cDNA is made from RNA and nobody will be doing BRCA sequencing from RNA. It will all be from isolated DNA.