Can someone with a history of bundle branch block convert back to sinus rhythm?

Not a rhythm problem. Bundle branch block is an anatomic or physiologic problem in conducting electrical impulses in part of the hearts conduction system. It is not a rhythm disturbance though it can be related to rhythm disturbances. Bundle branch blocks commonly exist with normal sinus rhythm.
Not really related. Conduction system of heart is as follows. Sa node is in the rt atrium.This fires & the impulse travels to the av node just above the venticles. There is a slight delay .Then the impulse goes to the vetricles via the bundle branch system. The left bundle to the left ventricle and rt bundle to the rt ventricle. So while fast rates can cause a rate depend bundle block , no opposite relationship.