Should the body of one who abandons prayer be treated as a Muslim or a disbeliever in terms of the ruling on exhuming it from the grave, and is it permissible to exhume the grave of a disbeliever to reveal the signs of torment and publicize them for admonition?

The grave of a disbeliever (kafir) is not exhumed. As for one who abandons prayer out of laziness, some scholars do not consider him a disbeliever whose disbelief expels him from the fold of Islam. It is not known that anyone among those who abandoned prayer in any era was not washed, prayed over, or buried in Muslim cemeteries.