The good/bad Snape debate and Harry's unfreezing

[snorkackcatcher]

A brief thought -- probably not original, so I would be interested to hear from any Snapecast listeners or the like -- sparked by travisprinzi's essay on The Great Snape Debate book in which the following comment was made:

I still have a hard time believing that Dumbledore would command the use of an unforgivable curse. This is why some version of Stoppered Death needs to be added into the theory; otherwise, you get terrible character inconsistency with Dumbledore.

At first I read this as it being a very bad reflection on Snape if he would be able to successfully cast the Killing Curse on Dumbledore (although on reflection I think 'Stoppered Death' here is the theory that Dumbledore was already dying painfully from the cave potion, which was the one Snape mentioned back in Book 1, and therefore Snape using the AK wasn't outright murder). That would be a fair point.

However, assume for a moment that the AK can almost-but-not-quite work in the same way as Harry's failed Crucio on Bellatrix -- a possible interpretation, given her statement that you have to mean the Unforgivables for them to work properly, and Fake!Moody's 'nosebleed' comment. Is there any evidence that Snape's curse on Dumbledore could have failed in this way? Possibly, yes. The wording of the end of ch.27 and beginning of ch.28 of HBP is suggestive:

A jet of green light shot from the end of Snape's wand and hit Dumbledore squarely in the chest. Harry's scream of horror never left him; silent and unmoving, he was forced to watch as Dumbledore was blasted into the air: for a split second he seemed to hang suspended beneath the shining skull, and then he fell slowly backwards, like a great rag doll, over the battlements and out of sight.

-----

Harry felt as though he, too, were hurtling through space; it had not happened ... it could not have happened ...

'Out of here, quickly,' said Snape.

He seized Malfoy by the scruff of the neck and forced him through the door ahead of the rest; Greyback and the squat brother and sister followed, the latter both panting excitedly. As they vanished through the door Harry realised he could move again; what was now holding him paralysed against the wall was not magic, but horror and shock. He threw the Invisibility Cloak aside as the brutal-faced Death Eater, last to leave the Tower top, was disappearing through the door. [emphasis mine]

If the curse itself didn't kill Dumbledore, then it was presumably the fall from the Astronomy Tower that did so, yes? In which case, the point at which Harry realises he can move again may be significant. The passage is written in such a way as to suggest that he could have moved at any time from when the AK hit -- but it doesn't actually say that, and could it be that it's literally at this point when the curse lifts? In other words, that it happens when Dumbledore hits the ground?

ETA: On taking another look at the passage, it struck me that Harry not being able to scream, and being forced to watch "silent and unmoving" as Dumbledore is blasted over the wall, is actually another point that supports the idea. It's speculative, admittedly, but the sort of long shot worth a small wager. :)