First of all, thank you a lot for such a detailed explanation. To be honest it's a little bit more than I can chew with my current level of English. Anyway, I'll be coming back to it time and time again until I can fully grasp it. What I got from it at the moment is:

1. "I will have failed if I haven’t given .." this is kind of future projection from the well known conditional form "I would have failed if I hadn't given .." and it makes sense for me.

2. "In essence, the statement that you have written above is basically stating that, at some unknown or unspecific or unimportant time in the future, I have failed at some specific goal on the condition that I have not yet been able to give you the confidence and desire to explore."

This is a very understandable explanation. I wish I could get the same for the "future conditional" because although I know the grammar rules for "future conditional" it still sounds strange for me that apodosis is in the future while protasis is in the present simple form. I always keep it in mind but still can't understand it naturally like I did from your explanation for "will have done/have done" form. But it would be probably another question.

3. As I understand "I will fail if I should / do not give" is absolutely equal to the sentence from my question although I have never met it with "should".

4. The form with "the future perfect" is kind of obsolete and is not often used in modern English.

So, the sentence from my question can be referred as "Future Conditional" as well?

For the most part, you are correct. I wouldn't say this construction of the future perfect is obsolete; I would say that this is just not so common, but it's still said. What's obsolete is the use of the present perfect subjunctive in the protasis ("if he haven't given"), but they still correlate, which is why I've compared them. I use the "should" there to replace the present subjunctive in that example. Another one would be: "If anything should go wrong, you may call me at this number." "should" forecloses the present subjunctive.

Read my addendum to my answer above for your failure to understand why the apodosis is in the future simple and protasis is in the present simple; plus, look at my answer here: ell.stackexchange.com/questions/151885/…

Now I can remember about "should", I learnt it, marked and then forgot. It was just a short note: Merphy R., English Grammar in Use, 4-ed.. Was "should" used in English of yore or it's just, as you said, a middle ground in Modern English? BTW, I surprisingly couldn't find the word "truckle" neither in Longman nor in Cambridge dictionaries. thefreedictionary.com seems to be more comprehensive in this case.

Yeah, its not very common, but "truckle" is a word, though. "should" is used more often now to replace the subjunctive. Back in the day, the present subjunctive was used more, so "should" wasn't so common then.

[ if you should have any more questions, please feel free to ask and I shall try to respond as quickly as possible as long as it not be too late in the evening.] So, I can say "as long as it should not be too late" and "as long as it is not too late" as well?

[q]What's obsolete is the use of the present perfect subjunctive in the protasis ("if he haven't given"), but they still correlate..[/q] Do you mean that the next sentence is correct too? * "I will have failed if I don't give you the confidence and desire to explore further ..."*

"as long as it not be too late" is very archaic English, but I said it to show you how English has changed since even as recently as Charles Dickens' times in the example above: "if the courses be departed from". You could say it that way to be a little archaic and people might give you a strange look and you could say it with "should" there and that's very formal. Most people say it, "as long as it is not too late" = "if it is not too late"; "as long as it should not be too late" = if it should not be too late"; "as long as it not be too late" = "if it not be too late".

Yes, that next sentence with "don't" sounds fine. The writer did not have to put it in the present perfect there. Using "don't give" there is more direct than using "haven't given" in the example above, but, for the most part, they would mean the same thing.

The average native speaker would probably find it to be incorrect because he is not familiar with this form; others who are familiar with this form may find it archaic or pretentious ("as long as it not be"), but no one would find anything wrong with "as long as it should not be"; the average native speaker would just find this to be very formal as it's the middle ground between the indicative and subjunctive form here.