... is hell an everlasting horror where the wicked burn forever?
I rather think Isla in particular, the Abrahamics broadly, and religions generally, paint quite nuanced pictures of the eschaton, about which we know nothing in any concrete detail.
So when we run with infernal images of everlasting horror, etc., we are rather speaking only of the (sometimes over-passionate) emotions, rather than the cooler light of the intellect.
Having said that, it's a given that the population as whole responds very poorly to the intellect, we are driven by, and often the prisoners of, our emotions and especially our passions.
Or is universal salvation possible?
"with God, anything is possible", as the Christian Scriptures have it (Matthew 19:26)
Or are all of the above irrelevant because the mystic understands God in a way that transcends such notions?
Understanding in a way that transcends does not necessarily mean that the idea, or the image, is untrue?
We have to be cautious of assuming mystics 'think outside the box', as it is often the case, or at least it seems that way to me, that the mystic sees deeper into 'the box', rather than the populist assumption that somehow the mystic has risen above it.
As a by-word, 'thinking outside the religious box' rather denotes a failure to fully comprehend religion as such, as religion deals with the Infinite and the Eternal. Indeed, by comparison, every other human pursuit is necessarily boxed by the nature of its object.