It won't so much as "go bad" as it will lose taste, color, odor and so forth. You can lose some trichs once it becomes too dry due to physically falling off of the bud, that would be the only drop in potency (besides an actual chemical half-life which would be unknown to me).
If oyu store it in a good air-tight jar or vacuum seal it it should last you for a good couple years with little to no ill effects.