What exactly do you mean with utility here? The Quasi-negative utilitarian framework seems to correspond to a shift of everyone’s personal utility, such that the shifted utility for each person is 0, whenever this person’s live is neither worth living, nor not worth living.
It seems to me, like a reasonable notion of utility would have this property anyway (but i might just use the word differently than other people, please tell me, if there is some widely used definition contradicting this!). This reframes the discussion into one about where the zero point of utility functions should lie, which seems easier to grasp. In particular, from this point of view Quasi-negative utilitarianism still gives rise to some for of the sadistic-repugnant conclussion.
On a broader point, i suspect, that the repugnance of repgugnant conclussions usually stems from confusion/disagreement about what “a life worth living” means. However, as in your article, entertaining this conclussion still seems useful in order to sharpen our intuition about what lives are actually worth living.
I would say the utility of a person in a situation S measures how strongly a person prefers that given situation, independently from other possible situations that we could have chosen. But in the end the thing that matters is someone’s relative utility, which can be written as the utility minus a personal critical level. This indeed reframes the discussion into one about where the zero point of utility should lie. In particular, when it comes to interpersonal comparisons of utility or well-being, the utilities are only defined up to an affine transformation, i.e. up to multiplication with a scalar and addition with a constant term. This possible addition of a term basically sets the zero point utility level. I have written more about it here: https://stijnbruers.wordpress.com/2018/07/03/on-the-interpersonal-comparability-of-well-being/