This reminds me of one of my favorite anecdotes. I wish I could remember the names of the two critics and the exact quotes, but the exchange went something like this. First Critic: The Inferno is totally unrealistic. For example, about three-fourths of the people Dante meets in Hell are Italian!" Second Critic: “That seems about right.” In any case, I imagine a modern retelling would have to be much more ethnicly diverse.
The Purgatorio is certainly interesting - but I’m not convinced that the lesser quality of the Paradiso is due to Sayer’s death, as much as the work itself. Even Dante had to be getting tired of it by that point! Sayer’s collaborator, Barbara Reynolds, had to complete, if I recall correctly, only the last thirteen cantos. They rest is Sayers. Declining Sayers, but Sayers.
The Ciardi is good, and comprehensible, where Sayers is sometimes a bit obscure, but, just as a read, the Sayers is much more enjoyable.
As a total aside, have you read the Jill Paton Walsh Peter Wimsey novels? Not Sayers (who on Earth could be?) but not bad.