Shape key reset?

I have created shape keys that are controlled by the rotation of an armature. Is it possible to have the shape key value slowly reset to zero automatically after the armature has been rotated?

I sort of forgot how drivers work, but these are driven shape keys, right? Is there any way you can key the influence of the driver?

Yes, but I was wondering if there was a way to set it up so that it would happen automatically without me needing to animate it.