Дегустация Horn of the Abyss

This practically doesn't change anything and doesn't answer many of the questions asked...

Well, I answered the only question that isn't obvious from what's written above.

That is, if in the conditional fifth round, someone from the "winners" bracket suddenly drops out, then instead of him...

No, because "you can only enter as a replacement in the losers bracket." If a winner drops out, they get a tech loss, fall into the losers bracket, and pass their slot to the player entering as a replacement.

...a player who dropped out in the conditional first round will suddenly appear???

No, because "the advantage is with those who have advanced further."

Or will the second chance go to the one who dropped out in the fourth round, since he advanced further (based on what is written above)?

Yes. Only there it will rather be someone who dropped out in the 6th or 7th round (having played them in advance).

Or is there a difference between "withdrawal and disqualification" and the fact that a dozen participants dropped out in the first round... So, they didn't withdraw or get disqualified, and no replacement is needed for them?

The difference is that "since the initial confusion is over, we will start playing more organized from the 2nd round," that is, all of the above starts working from the 2nd round. If you transfer the places of all the missing newcomers, then the first dropout from the tournament will happen very soon...

And what is the point of these replacements in general?

Fewer technical results in the bracket, more game results. And also, an incentive to independently find opponents for the next rounds, relieving some of the burden from the organizer.

This isn't entirely fair, doesn't anyone think so?
That is, some play until 2 losses, and others until 4?

Players who enter as replacements play until 3 losses, because "you can only enter as a replacement in the losers bracket." In my opinion, the extra "life" fully corresponds to the benefit to the tournament from playing matches early.

Or does the one who enters as a replacement have to win twice against his opponent, while the opponent only needs one win?

No, he plays as usual.

You can only enter as a replacement until a certain round, and if Vic decided to do so, he should announce until which round.

You can enter as a replacement at any time, as long as there are free slots. Closer to the final, players usually don't drop out.