Is everyone that falls into major shirk considered a polytheist, and are the rulings pertaining to the polytheists applied to him? May Allah reward you with good.
Yes, whoever disbelieves in Allah then he is a kaafir, and likewise the one who makes shirk with Allah then he is a mushrik. Just as the one that believes in Allah is a muwaahid (one who singles out Allah alone in worship) mumin (believer). As for the one that the message never reached him, then he is not called a believer nor a disbeliever, and is not to be dealt with as a Muslim, rather his affair is with Allah on the day of judgement. These individuals are those who were ignorant and the message never reached them. So they will be tested on the day of judgement. However as for the one that heard about Islaam and did not believe and did not except Islaam then he is a disbeliever and a enemy of Allah.
Source: Fataawa Al-Allaamah Ibn Baaz (Rahimahullah) pg.77
Translator: Muhammad bin Adnaan Abouharb
Islaamic University of Al-Madeenah