Favours in stories tend to be weird. They're often way too one-sided. Which direction depends entirely on what's needed for the story. Quite often the MC does a lot of work for people without getting much in return, and in other stories they're gifted a lot of unearned stuff.
True that. But I feel in this case that the MC has earned a great deal of favorability from this wight. He delivered something the dead don't always get: Justice. Not only for the wight, but also for the entire village he oversaw. That is a huge freakin' deal because now, even if someone were to purify them, they'll be able to go without any real regrets.
I would say that if the MC needs another favor from this wight later on down the road, then he'll probably get it... But he'll need to make sure that the metaphorical "interest rate" isn't more than he can handle.
