I already answered your question and it's not a simple black/white answer either.
If it were my child I would hope that we would have the level of communication where my child could confide in me about something like homosexuality. But that is not always the case in many families and acceptance of that is highly variable. If my child could not - I would hope that there was an adult that he could trust enough to talk to and get advice from.
As a parent I would want to know, but then, as a parent I would have no problem with homosexuality. What if I did though? What if my husband despised gays? What if the home situation was one in which the child could not go to his parents? See it's not just the parents and their rights, it's also what is best for the child and none of us here know that - we don't know the situation.
You talk about tragic consequences but have you thought about the possibility of tragic consequences in informing the parents that their child is not only having sex but - is also homosexual? And this was 20 some years ago?
They are valid questions, but they are questions without clear cut answers requiring a lot of personal judgement.
And, by the way...I previously answered...guess you don't read to well