I also completed the Forbidden vault. Was not able to solve the scrolls puzzle and 3 items puzzle, my understanding it's not possible if you don't have all the required items on you.
I also saw an altar at the 'spiritual' plane, did not tried to find a way to it b/c was already very frustrated by save/loading, that place is way too tough IMO.
And the first encounter with Demiosis also forced me to save/load too much for a comfortable game experience...
I'm currently right before the battle with two resurrected minions of Demiosis... and I already feel a bit bored by it
