(1)I spent a lot of time on the subject of idolatry and in fact it looks to me that  for a person to "tie himself to a tzadik" is not idolatry. At least based on the Talmud in Sanhedrin  from pages 60 to 63.
(note 1)
(2) We have four types of idolatry not like the way of an idol. And we have serving it according to its way. But being attached to a tzadik does not seem like a way of serving the tzadik any more than doing any mitzvah to bring oneself closer to God. Conceptually it seems different. But that is not news to anyone.

(3) What is news is that after going through the subject matter as thoroughly as I could it seem to me that the whole approach to idolatry in those pages of Sanhedrin does not seem to have anything to do with being attached to a tzadik.

(4) But certainly some people do worship a tzadik. That  is bad. But attachment is not worship. And the general attitude is that the tzadik should pray for one and by that one is helped. It seems very far away from praying to the tzadik. So I would have to say that the Nefesh HaChaim was exaggerating when he said attachment to a tzadik is idolatry. (note 2)

(5) Of course what chasidim do is idolatry, but not because of attaching themselves to a tzadik. Rather because of worship of a person they think is  a tzadik. And not to confuse the issue the case is usually the object of worship is most often a "rasha" highly wicked and highly clever at using his position for nefarious purposes.

(note 1) In Avoda Zara 41 it says, when an idol falls and breaks it is nullified. Rav Shach derives from that that the major thing that causes something to be an idol is the thought, "This can help" in an invisible sense. But there too just because one thinks, "This can help" that alone doe not make it an idol.

(note 2) This is not the only place in which the Nefesh HaChaim exaggerated. Also in where he says if the world would be empty of words of Torah for a second, it would be destroyed. Reb Chaim Kanievsky [Bnei Brak] pointed out that the Talmud says in one place that the world was in fact empty of words of Torah for a second.

In any case, if we understand Torah in the sense that Torah is hidden inside of everything. Torah is the interface between God and his creation.