Last week the Bills hinted that they will tweak, but not fundamentally change, their helmet; promising to keep the charging buffalo but letting on nothing else about possible changes to the headgear.  A quick glance around the league reveals five teams that have recently updated their helmets.  The Cardinals, Falcons, Dolphins, Eagles and Lions all spruced up their logos, mostly by fattening the outlines and/or adding extra shades of the base color to create a mild 3d effect.  One can envision an update of that style to the Charging Buffalo, involving new shades of blue to add some texture.

As for the uniform, some other teams' jerseys provide a template for the incorporation of an alternate logo.  The standing Buffalo might appear on the shoulders like on Philadelphia's jersey, or off to the side on the chest like the Jets have.  

Quickly after the Bills' announcement, WGR's Jeremy White predicted that the team would go with a white helmet with the current logo and, as he puts it, the "AFL style throwbacks that we've all really LOVED the last few years."  That sounds like as good an approximation as any, and White even hints that he's gotten an early look.  However, I think you have to assume the new jersey will be changed beyond a simple full time return to the throwbacks, even if it is reminiscent of them. These changes are made to sell jerseys, not for fans to just go dig out one they already have.