The spell ends if the ring is removed

Warding bond has a very specific material component.

The section on material components states:

...if a cost is indicated for a component, a character must have that specific component before he or she can cast the spell.

As a general rule, I would say that once a spell is cast, the materials used to cast it no longer need to be considered. However, warding bond is different from other spells in this wording on the material component (emphasis mine):

a pair of platinum rings worth at least 50 gp each, which you and the target must wear for the duration

I would rule this as a case of specific-beats-general in that the use of the word "must" indicates that the duration is directly linked to the ring being worn, and thus the spell ends immediately upon removal of the platinum ring(s).