I took a look. I found this quote:

This might seem reasonable at first - it is a strangely appealing image - but something very odd is going on here. My experiences are switching from red to blue, but I do not notice any change. Even as we flip the switch a number of times and my qualia dance back and forth, I will simply go about my business, not noticing anything unusual.

This seems to support an answer of:

2: You'd likely not notice anything, because if you did, a P-Zombie would not be just like you.

But if that's the case, it seems to contradict the idea of red qualia's existence even being a useful discussion. If you don't expect to notice when something vanishes, how do you have evidence that it exists or that it doesn't exist?

Now, to be fair, I can think you can construct something where it is meaningful to talk about something that you have no evidence of.

If an asteroid goes outside our light cone, we might say: "We have no evidence that this asteroid still exists since to our knowledge, evidence travels at the speed of light and this is outside our light cone. However, if we can invent FTL Travel, and then follow it's path, we would not expect it to not have winked out of existence right as it crossed our light cone, based on conservation of mass/energy."

That sounds like a comprehensible thing to say, possibly because it is talking about something's potential existence given the development of a future test.

And it does seem like you can also do that with Religious epiphenomenon, like souls, that we can't see right now.

"We have no evidence that our soul still exists since to our knowledge, people are perfectly intelligible without souls and we don't notice changes in our souls. However, if in the future we can invent soul detectors, we would expect to find souls in humans, based on religious texts."

That makes sense. It may be wrong, but if someone says that to me, My reaction would be "Yeah, that sounds plausible.", or perhaps "But how would you invent a soul detector?" much like my reaction would be to the FTL asteroid "Yeah, that sounds plausible.", or perhaps "But how would you invent FTL?"

I suppose, in essence, that these can be made to pay rent in anticipated experiences, but they are only under conditional circumstances, and those conditions may be impossible.

But for qualia, does this?

"We have no evidence that our qualia still exists since to our knowledge, P-zombies are perfectly intelligible without qualia and we don't notice changes in our qualia. However, if we can invent qualia detectors, we would expect to detect qualia in humans, based on thought experiments."

It doesn't in my understanding, because it seems like one of the key points of qualia is that we can notice it right now and that no on else can ever notice it. Except that according to one of its core proponents, we can't notice it either. I mean, I can form sentences about FTL or Souls and future expectations that seem reasonable, but even those types of sentences seem to fail at talking about qualia properly.

Wait, those premises just seem wrong and contradictory.

1. To even work in the thought experiment, p-zombies live in a world with physics and logic identical to our own (with possibility of added components).
2. In principle, qualia can either be generated by physics, logic, or something else (i.e. magic), or any combination thereof.
3. There is no magic / something else.
4. We have qualia, generated apparently only by physics and/or logic.
5. p-zombies have the exact same physics and logic, but still no qualia.

???

My only remaining hypothesis is that p-zombies live in a world where the physics and logic are there, but there is also something else entirely magical that does not seem to exist in our universe that somehow prevents their qualia, by hypothesis. Very question-begging. Also unnecessarily complex. I am apparently incapable of working with thought experiments that defy the laws of logic by their premises.