I think it's possible here, but hardly necessary. Future perfect has its uses-- for events or actions for which we need to emphasize duration or completion in the future: ' by the time you read this posting, I will already have gone to work ', stressing the completion of my departure before your future reading (since I have not posted it yet in my real time, all is in the future, and my departure is definitely before your reading-- hypothetically, of course). In your example, however, the losing of respect can hardly come before the knowledge of the fall from grace, so a simpler 'I will lose' seems sufficient to me-- or perhaps we need to be consistent not with real time, but with the tense of the action-- 'I have lost all respect for you if you did'.
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