Those who were once considered upon the salafī methodology but then deviated from it; is it lawful for us to listen to their audio recordings or read their books that were written previously as well as their lectures?

Shaykh Muqbil ibn Hādi al-Wādiʿī:

I do not advise with the reading of their books or listening to their recordings. I find the following statement of Shaykh al-Islam Ibn Taymīyyah –may Allah ﷻ have mercy upon him- to be amazing. He said: “Had Allāh not produced al-Bukhārī and Muslim…” And al-Bukhārī and Muslim are two individuals who are both considered Shaykh al-Islam. Scholars whose superiority has benefited Islam and the Muslims; their two books represent the most authentic books after the Book of Allah ﷻ He said: “Had Allāh not produced al-Bukhārī and Muslim, His religion would not have been lost.

So Allah ﷻ has certainly preserved His religion as He says:

۞ إِنَّا نَحْنُ نَزَّلْنَا الذِّكْرَ وَإِنَّا لَهُ لَحَافِظُونَ

Certainly, We have sent down the reminder, and surely, We will preserve it.” (Q 15:9)

So I advise you to stay away from their books and recordings, and Allah’s refuge is sought, as well as attending their lectures while they themselves are in need of being called to back to the Book of Allah and the Sunnah of His Messenger and to repent to Allah ﷻ from what emerged from them during the issue of the Gulf [war] as well as other matters.