The oldest brother had a rough sort of vindication. Targum Pseudo-Jonathan on Genesis 42:22 preserves Reuben's statement: "Did I not tell you, saying, Do not sin against the youth? But you would not listen to me; and thus, behold, his blood is required of us."
Reuben's original warning
At the pit in Dothan, Reuben had tried to save Joseph. Genesis 37:21-22 records him arguing the others down from murder: don't shed blood, throw him in the pit, I will come back for him. The plan was to rescue Joseph later. When Reuben returned to the pit, Joseph was gone — already sold by the other brothers in his absence (Genesis 37:29-30). So when Reuben now stands in an Egyptian prison saying "did I not tell you," he is not lying. He actually did tell them.
His blood is required of us
The Aramaic paraphrase, whose final redaction belongs to the Land of Israel around the seventh or eighth century CE, preserves the terrifying phrase: blood required. This is the language of Genesis 9:5, God's covenant after the flood: "your blood of your lives will I require." Reuben believes Joseph is dead, and he believes the brothers are now standing under divine accounting for that death. What he does not know is that Joseph is standing ten feet away, listening through an interpreter, hearing his oldest brother try to take moral inventory of the crime.
The takeaway
Sometimes the people who warned us get to say "I told you so" — and it is not petty; it is part of how a family begins to tell the truth again.