If Harry ever has an extraordinary need to manipulate Lesath, he could play it off something like “You dare to complain to your Lord, after he saved one of your parents to show his generosity and mercy? When you hadn’t yet done a thing for him? If you want your father’s freedom, earn it! Serve me faithfully, and you shall be rewarded as you deserve.”
That would be an interesting scene - ‘you saved my mother; why didn’t you save my father, Harry?!’
Would Lesath feel bound to serve Harry just for Bellatrix’s rescue? Maybe. IIRC, child psychologists find that kids bond with the mother more.
If Harry ever has an extraordinary need to manipulate Lesath, he could play it off something like “You dare to complain to your Lord, after he saved one of your parents to show his generosity and mercy? When you hadn’t yet done a thing for him? If you want your father’s freedom, earn it! Serve me faithfully, and you shall be rewarded as you deserve.”
I can’t imagine he’d go that way—way too ‘dark lord’. I could see him taking this opportunity to try to convert Lesath again though.