Would Voldemort have lost his powers if he hadn't made so many horcruxes?

Question

I am currently rereading all the books, and a previously overlooked yet certainly key distinction keeps coming up: the reason for Harry's survival vs. the reason for Voldemort's loss of power.

In the first chapter of COS, we read that:

"Harry had escaped with his lightning scar, and somehow--nobody understood why--Voldemort's powers had been destroyed the instant he had failed to kill Harry" (COS, 4, hardcover).

Much later in the book, when Harry encounters Voldemort's diary-held memory, he reiterates:

"No one knows why you lost your powers when you attacked me...But I know why you couldn't kill me. Because my mother died to save me" (COS, 316, hardcover).

It is there established that Harry survived the Killing Curse due to his mother's sacrificial protection. Common sense would dictate that the rebound of this Killing Curse was what left Voldemort a shell of his former self and made him lose his powers. However, that is clearly not the entire case, as we keep hearing "no one knows why you lost your powers" from a person that knows why he, himself, survived.

Finally, in DH, we get some clarity from Dumbledore about a possible contributing factor: the Horcruxes.

"He had rendered his soul so unstable that it broke apart when he committed those acts of unspeakable evil" (DH, 592, hardcover).

And from JKR herself:

"It was just that [Voldemort] had destabilized his soul so much that it split when he was hit by the backfiring curse" (Pottercast Interview, 2007).

Thus, it is at least implied if not outright proven that Voldemort's loss of power had something to do with more than simply the rebound, but also the degree of destabilization his soul had experienced to this point.

My related questions are therefore:

1. Would Voldemort have lost his powers if he hadn't previously made 5 horcruxes? In other words, would a rebounded Killing Curse not necessarily strip the culprit of his/her powers?

2. Would it have been different if he had only made 1 Horcrux (not "so unstable")?

3. Finally, am I looking into this way too much? Did Harry simply fail to equate the causes of his survival and Voldemort's downfall, and did Voldemort lose his powers simply because of the rebound?

Answer 1

1. Yes
   Voldemort is not immune to Avada Kedavra, it's just that no one has been able to try it on him and live to tell the tale. In OotP we see that even Fawkes can get destroyed by it. Voldemort lost his power because he was hit by the killing curse, the reason he didn't die was because his soul had been kept Earthbound by his horcruxes.

2. Probably
   Voldemort is the only known wizard to have made 7 horcruxes in Potterverse. We see that even talking about horcruxes is frowned upon in Hogwarts and possibly not many people even know how to do it, or that such a thing as horcrux even exists, (we never even hear the word until HBP). It is only Dumbledore's guess that his soul had become so unstable that it got chipped off unintentionally when he failed to kill Harry. If he had made only 1 horcrux, maybe a part of it wouldn't have latched on to Harry, but the rebounding Avada Kedavra would still have destroyed his body, stripping him of his powers.

3. Most probably Yes, Voldemort lost his powers simply because of the rebound, and would have lost them even if he had made just 1 or 0 horcruxes (in the latter case he probably wouldn't have survived to regenerate either).

Answer 2

Yes, because the Dark Lord lost his powers upon losing his body.

The Dark Lord had lost his powers when he lost his body, due to the limitations of having a spirit form. His losing his powers was directly because he was ripped from his body, and left incorporeal.

“Nevertheless, I was as powerless as the weakest creature alive, and without the means to help myself … for I had no body, and every spell which might have helped me required the use of a wand …”
_{^{- Harry Potter and the Goblet of Fire, Chapter 33 (The Death Eaters)}}

It’s not a result of how many Horcruxes he had, because Slughorn said that the soul would exist in such a form after being killed while having one Horcrux. Slughorn never even considered the possibility of multiple Horcruxes until Tom brought it up, so he clearly meant that having only one Horcrux would mean if the body was killed, the wizard’s soul would exist in an incorporeal form.

“Well, you split your soul, you see,’ said Slughorn, ‘and hide part of it in an object outside the body. Then, even if one’s body is attacked or destroyed, one cannot die, for part of the soul remains earthbound and undamaged. But, of course, existence in such a form …’

Slughorn’s face crumpled and Harry found himself remembering words he had heard nearly two years before.

‘I was ripped from my body, I was less than spirit, less than the meanest ghost … but still, I was alive.”
_{^{- Harry Potter and the Half-Blood Prince, Chapter 23 (Horcruxes)}}

If the Dark Lord hadn’t made so many Horcruxes, he’d still have lost his powers, since that was a result of him losing his body, which would still have happened if he’d made less Horcruxes.

It’d only be different in that his soul piece mightn’t stick in Harry.

What was likely caused by the Dark Lord’s soul being particularly unstable is that a piece of his soul broke off and stuck in Harry, since that only had happened because of how unstable it was.

“You were the seventh Horcrux, Harry, the Horcrux he never meant to make. He had rendered his soul so unstable that it broke apart when he committed those acts of unspeakable evil, the murder of your parents, the attempted killing of a child. But what escaped from that room was even less than he knew. He left more than his body behind. He left part of himself latched to you, the would-be victim who had survived.”
_{^{- Harry Potter and the Deathly Hallows, Chapter 35 (King’s Cross)}}

It’s possible that if the Dark Lord hadn’t made so many Horcruxes and his soul wasn’t so unstable that it wouldn’t have fractured when the Killing Curse hit him, so wouldn’t have stuck in Harry.