I think that when it comes to those who are left behind all that anyone can do is write a note explaning that suicide was what they wanted so that those left behind are less likely to be left with as many unanswered questions.
Telling other people in advance about plans/wishes to die before one has left would always be a terrible idea as in this anti-suicide society other people would very likely try and interfere in plans to die, sadly. But the fact is that we all have to die someday and eventually we very likely won't even exist in the memories of those who continue to stay here and that's just the reality, whatever happens in this world after we are gone could never be our concern.
And when it comes to the individual, I think that many people go through with ctb when they find a method that they feel confident in and they just get so determined to be gone, suicide certainly isn't straightforward in this world.