I would say Limbo. Clearly the theologians cited by De Lugo distinguished between justification and salvation (as Father Feeney did), but I don't recall or haven't read what they say about someone who would hypothetically die justified but not saved.
So my answer is Limbo. Father Feeney simply answered "I don't know." I am unaware of whether these other theologians dealt with the question at all.
Fr. Feeney said: "There is no one about to die in the state of justification whom God cannot secure Baptism for, and indeed, Baptism of Water".
He also said: "Unbaptized infants who die go to Limbo. Notice, they do not go to Hell. Also notice, they do not go to Heaven. Unbaptized adults who die go to Hell. Notice they do not go either to Limbo or to Heaven".
Which is what I believe and is akin to saying no one dies justified and unbaptized, i.e. God will provide the sacrament to all who are in the state of justification before they die.
I do not believe justification is obtained at all without the sacrament, but if such a thing were possible, it seems against Catholic reason to think that God would take that person before having him baptized. And what good would it do anyone to be in the state of justification and die without baptism? I mean, to miss heaven at all is to miss it completely and as he said, adults who die unbaptized go to hell.