Update reviewer state to Closed when Author/SME decides to close the review

I haven't tried this but you may be able to accomplish that by changing your role settings - fix it to only require 1 author, and not require the other roles (reviewer, etc) to mark reviews finished / wait for them to mark finished before changing phases.  That way the author is the only approving role and the review record would always move to the completed phase when the author approves it.