There was already 'coincidence', such that attracted the infantophage skyship goblins, and the "don't revisit the moment" rule that the Doctor inexplicably found to be a deal-breaker (he could have gone back and landed
around the next corner; after all, Nine freely did that (with impetuous Rose, but this time he had no worry about the Companion creating the paradox and sunmoning the chronovores). If there's no actual mystery left (and in this case it seems it might indeed be "sometimes a cigar is just a cigar"), it's not for want of misunderstandings all round.
(And Mrs Flood, chanelling a Scary Poppins[1], may yet be the instigator of some of this. Hard to tell where she lies on the Harbinger/Puppet to Big-Bad scale; with also
possible outcomes including Anti-Villain With A Heart Of Jerk.)
We have supernatural (or 'supranatural') leakages all the way through this Giggle-onwards story-arc. So, yes, apparently expectation can do wonders.
The whistle was the incarnation of the mini-multi-Tardis's rather mixed up mechanics, I think. We've had vital portable bits of equipment disgorged from the Tardis console before (at least one Sonic!), though this was sort-of-behind-a-eort-of-Roundel, which also seems to be a call-back (and not just to post-Giggle duplication-mallet).... Or just as much a no-frills 'plain old signal' as Ten's door-opening finger-snap.
((Postscript: I've since learnt that the whistle was even more Timey-Wimey. It was cut from the script/filming, but at the end of the episode, I think at some point when the 'dog leashing' was largely accomplished, the Doctor then (was to have) opened a his-Tardis floor-hatch (something like where he got the duplicator-mallet) and dropped the whistle in... and through to the Memory-Tardis,
at the point of time it dropped out of the ceiling-hatch... Paradoxen, eh?
))
Destroying the Destroyer (in the Time Vortex, moreover, which can't be good for the old dog's 'historic permanence', now that he isn't just hitching a ride like Captain Jack) seems almost the
only way to undo Reality Changing damage.
And last time, wasn't he just injected into the vortex? Which is noted to not be Instant Death for Sufficiently Beyond-Mortal Beings, though certainly intended to 'not be nice', and easy to be lost in (if you're not a slecific creature lf the vortex). This time, he was dragged against its walls. At the very least, to cut into the 'wrong realities' of all the Dusted Eras that his cross-time influence had caused to be, but the transitioning between reality and vortex tends to be the most harmful bit, and certainly not something to be attempted without actual time-tech 'protections' (which doubtless were dialled up in order to take Sutekh there, then dialled back in order to do the damage once in it).
[1] Mary Poppins, but reversed in many ways... 'always' there rather seen to arrive out of nowhere, asked to take care of a parent rather than offering to take care of children, not exactly being helpful/doing-what's-needed when ledt to it, seems to have affinity to snow, not fine (if windy) weather, and doing so wearing a white fluffy outfit (holding a white brolly - that
doesn't talk!) rather than mostly plain black (with largely 'audience avatar', if habituated with magic, umbrella)... Got to stop there, but there are plenty of other inverted characteristics...