Answer two simple questions:
Why are you killing this person before God completes what is TOTALLY His doing?
I didn't kill anyone.
If the person in the hypothetical scenario died in the state of grace, before having received baptism, God would have already completed what was necessary for him to be saved. Men are saved by sanctifying grace, not by the baptismal character. No one before Fr. Feeney held that the character was necessary for salvation.
The Sacrament of Baptism is absolutely necessary in its effect, but the effect can be received prior to reception of the Sacrament.
What exactly is this "desire to receive baptism", is it the explicit desire to be a baptized Catholic, the baptism of desire of the catechumen of St. Thomas? Or is it the implicit faith of a Muslim, Hindu, Jew?
The common teaching, as found in most pre and post Conciliar catechisms, is that
implicit desire for baptism suffices:
Catechism of Pius X:
17 Q. Can the absence of Baptism be supplied in any other way?
A. The absence of Baptism can be supplied by martyrdom, which is called Baptism of Blood, or by an act of perfect love of God, or of contrition, along with the desire, at least implicit, of Baptism, and this is called Baptism of Desire.
Countless Catholics who died after the Council of Trent saved their soul by believing what the Catechism of Pius X just taught. Whether any Feeneyite has been saved is an open question.