I love this game and have played it several times, but I have never actually finished it. What happens is, once the monastery quest comes around I end up getting frustrated and bored and end up killing everyone in the monastery and then, of course, the town guards get involved so they all die and after that I've got an insatiable bloodlust going on so I end up going town to town looting and pillaging. That's the canon ending to Henry's story in my world.
There's an easy hack to get around the buggy, railroaded monastery quest. Once you know the identiy of the fake acolyte, although the game won't allow you to utilize this knowledge in dialogue, you can find a dagger stashed away, sneak up on your target while he is alone, kill him with an automatic stealth dagger takedown, then pick up the required item from his corpse and continue on with the main quest.
Granted, the remainder of the main quest isn't much good, either.