I guess the next question is which franchise will continue to exist: Guitar Hero, Rock Band, or neither. The Hero brand has sold better every year except 2009, and Harmonix may switch to dancing games depending on how well Dance Central sells. If Activision ends up having no competition, they might release a game every year and have reasonable sales. If Kinect fails and Harmonix still makes Rock Bands, both brands might die. But Rock Band might die no matter what, considering Harmonix's 2009 layoffs and Viacom's trying to sell them off.
So long story short, I predict one Guitar Hero game a year from Activision until the end of time.
As a best case scenario.
Love and tolerate.