I'm literally inches away from getting to the Sky Temple, but one thing stands in my way. The Blood Seal (I didn't even know what this was until I youtubed it!).

Unfortunately, without the NPC to tell me what exactly it is, it will not show up, and this means I cannot activate it at all. I told them to go on ahead and I would meet them at the Sky Temple. This means they're long gone, and cannot be found anywhere. I fear my game is now impossible to complete as a result of this serious bug.

If it's a known issue, and has been resolved, can someone at least point me in the direction of a method to open the blasted door?