Well, there are two approaches.
First, the one that gives more glory to God but which might be kind of
unpalatable to most unbelievers and immature Christians. God does not
'send' anyone to hell, we earn that punishment ourselves by our sins.
We all have a conscience which tells us right from wrong and when we
go against God's law which is 'hidden in our heart' (Ecc. 3:11) we
deserve hell. So it is not that God is cruel in allowing some to go
to hell who have not heard the Gospel, it's more that he is extremely
gracious in allowing some to hear the Gospel, repent and believe and
be saved. I think of it like a lifeboat: you are in a lifeboat that
holds 10 people, you come along a sinking ship with thousands in the
water. You save 9 from death, since that is all you have room for.
Would you be held responsible for the other thousands that perish? Of
course not! You would be a hero. So, if someone does not hear the
Gospel and dies unsaved they deserved their punishment; those who hear
and respond deserve it too, their salvation was not earned by
believing, it was an act of grace.
But, I wouldn't share that with a new believer or unbeliever, hard to
understand, since they will argue that God's lifeboat is big enough
that all should be able to be saved and that he could saved everyone.
The other approach is to consider that God does reveal himself to all
people, though not all hear John 3:16. Romans 1 speaks of the fact
that none of us have an excuse to deny God since he is evident in
Creation. He has given us a conscience and those who go against it
have no excuse, again, from Romans 1. Those who follow their
conscience will be judged based on what they knew: they can do right
or wrong out of a desire to be obedient to God even though they may
not be able to call on the name of Jesus and be baptized, that is
found in Romans 2: 14(Indeed, when Gentiles, who do not have the law,
do by nature things required by the law, they are a law for
themselves, even though they do not have the law, 15since they show
that the requirements of the law are written on their hearts, their
consciences also bearing witness, and their thoughts now accusing, now
even defending them.) 16This will take place on the day when God will
judge men's secrets through Jesus Christ, as my gospel declares.
If you notice, they are still judged and saved by Christ, even though
it is their conscience which will bear witness to them. It's like
Abraham who was saved by faith in Christ, even though he did not know
the name of Christ, yet he believed in God's savior.
So, short answer, they will be judged by what they knew and how they
responded to the innate knowledge we have of God.
Your point is more important though: this guy has heard the Gospel, so
he has no excuse when he rejects the name of Christ, and will be held
to a higher standard, to those who much has been given, much will be
expected. He should not use this difficult subject as an excuse to
reject Christ.