The problem is that the story can indeed be damaged. I'm prevented from narrating a sword strike that drops a character to the game state of dying in 4E because a warlord might shout at them and prove my description of the sword stroke being a real injury to be a lie.
I don't agree that you're prevented.
Given the assumption that hit points represent a combination of factors, only one of which is physical health, there's no reason that someone can't lose hit points (narrated as a deterioration of physical health - wounds, injuries, etc), and subsequently regain hit points (narrated as a resurgence of willpower and determination).
If I narrate a nasty stab in the leg when I'm Bloodied, then just because I return to full hit points during our Extended Rest, that doesn't mandate that the wound in my leg is gone. I'm at full hit points; I also have a wound in my leg which will gradually go away over time. The wound was generated by the hit point mechanic, but it is not inextricably linked to the particular 15 hit points I lost at the time it was incurred.
Similarly, you might have a half-orc archer shoot several large arrows into the PC Fighter. On the one that drops him to Dying, you narrate one of the arrows sinking into his stomach. But he nevertheless triggers a power as a Reaction, which allows him to use his last Healing Surge and kill a few more orc minions. Did the Healing Surge render the shot to the gut narratively incorrect? Not at all. He still had the wound; the hit points his Healing Surge restored represented one of the other facets of the hit point pool.
Or it might make a sorcerer who is feeble in melee suddenly rush up to a fighter because the fighter's player pushed the "come and get it" button.
I see that as a blinkered view of the possibilities. Did the sorcerer decided to run up to the fighter to whack him with his stick? That seems implausible.
What if we narrate that the fighter cuts the rope holding the chandelier aloft? The sorcerer glances up to see it plummeting towards him, and with scant inches to spare, dives clear as the chandelier crashes to the ground. The sorcerer rolls back to his knees... and realises, as the pommel of the fighter's sword smashes into his teeth, that diving
towards the fighter might have been a hasty decision he'll come to regret...
What if we narrate that the fighter reaches down and yanks on the rug? The sorcerer, off-balance, stumbles forward to be clotheslined by the fighter's armoured forearm...
What if we narrate that the fighter rolls forward through the barrage of magic missiles, snatches the sorcerer by his lapels, and hurls him ten feet to crash to the floor... before striding back over and stabbing him as he struggles back to his feet?
Any of those could result in the tactical scenario that
Come And Get It declares must exist by the end of the power's resolution, and none of them need the feeble sorcerer to decide he's Tenser for no reason.
Or it might make a player wonder why they can't do something more than once in a five minute period when they've just demonstrated that their character can do it.
They demonstrated he could do it, given the combination of circumstances which existed in the cinematic depiction of the combat at that time, and which might not occur again for the rest of the encounter.
There's a shot in
Robin Hood: Prince of Thieves, where two men on horseback charge Robin. He pulls out two arrows, rips the fletching on one with his teeth, and shoots; the damaged arrow veers off-course, and one arrow hits each opponent.
Essentially the
Split The Tree power.
What if one guy was two feet left, and the other guy was two feet right? On the battlemat, they occupy the same five-foot squares... but in the cinematic portrayal of the scene, if the first arrow is on-target, the second arrow now misses by four feet!
So when Robin is attacked by two guys, Costner has a choice to make. If he expends his
Split The Tree power, they're in position for the ripped-arrow trick to be viable. If he doesn't, then they're out of position by a few feet - not enough to change the location of the minis on the battlemat, but enough that cinematically, he can only reliably aim at one of them.
Kevin Costner has narrative control via the use of the Power; Robin Hood, on the other hand, evaluates the position of the men and decides whether it's worth shooting two arrows. He doesn't know that they'll only line up nicely when Costner decides that they do, but when it happens, he recognises the opportunity to pull off the stunt.
-Hyp.