In the Kvatch Oblivion world, my character snuck into the place where that Imperial is being kept in a cage. She shot the Sigil Keeper with a poisoned arrow and legged it out of there back onto the ramp, turning around with another arrow nocked. As soon as she got onto the ramp, the battle music stopped and I thought the poison did its dirty work, so she snuck back in.

The Sigil Keeper was nowhere to be found. I checked the whole tower, thinking he fell onto the corpse masher, cleared the two daedra below, looked under the elevator platform, checked the ramp, checked the Oblivion world below the ramp, around the tower, nothing. The Sigil Keeper simply vanished, and now I can't get to the Sigil Stone.

Is there something I can do (I play on the PC, so console is an option) or am I forced to load the most recent save before stepping into the tower with the Sigil Keeper?

Perhaps of note: the Sigil Keeper didn't engage in conversation with my character. To her, having a talk with a Dremora takes second place to filling its face with arrows.

EDIT: typos.

Try player.moveto 00093EF0, that should teleport you to the Sigil Keeper. If it doesn't work, you can get his key with the console.

I get an invalid object reference error message.

I'll try it again in the tower, hang on.

EDIT: no banana.

I also tried tcl-ing around, he's nowhere in the tower or around it.

player.placeatme 00093ef0 worked, though!

Thanks!

If it doesn't work, try the same command as above but type 9504D instead.

I'm glad you solved it but try this first - player.moveto 878d5, that's the correct ID, I checked it in my game, looks like UESP has got it wrong. Placeatme is not so advisable to use because it can cause bloating if overused.