How to enter Nethack Quest if Quest Leader is killed?

I entered the Quest level wearing a ring of conflict. Subsequently the Quest Leader was accidentally killed by one of her (Valkyrie) disciples. Now I am unable to descent the stairs to obtain my Quest artifact (Orb of Fate) and the Bell of Opening. I've already gone through all of the dungeon levels (and found the vibrating square at the bottom level) short of killing the Wizard of Yendor to get the Book of the Dead. I am at experience level 27 and can freely teleport and teleport control. I tried wishing for the Bell of Opening in order to obtain the Amulet of Yendor, but only got a plain bell. Is there another way to descend to the Quest levels or get the Bell of Opening?

Unfortunately, there is no way to proceed if your quest leader dies:

If the quest leader is killed or level teleports before you get permission to go down, the game will also be unwinnable.

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