Question:

Is there anything wrong with saying that Abu Talib died as a non-Muslim?

Answer:

No, the Prophet alayhi salam himself mentioned that
Abu Talib will be in the least level of the hell-fire,
and even this would cause the brains to boil,
and if it was not for the Prophet’s intercession,
he would have been in the deepest part of the fire,
as is narrated in Bukhari.

Allah knows best.