There are various schools of thought about kagebunshin, about how the technique works and about why it's classified as a kinjutsu.
The most common explanation of how it works is that it evenly splits the user's chakra among all the copies. However, that doesn't seem to match very well with the way it's observed to be used, nor with Kakashi's ability (demonstrated during the Wave bridge fight) to create many more kagebunshin than Naruto with the same total amount of chakra, simply by being more efficient at applying it.
The most common explanations of why it's a kinjutsu are that it uses so much chakra (leading to chakra exhaustion or the like), and that the mental whiplash of regaining the memories of a popped or otherwise expired kagebunshin can be damaging, especially in extreme cases.
Let's consider a different model. Let's say that creating a kagebunshin does take a certain amount of chakra, and that you can waste more or less additional chakra in the process depending on your chakra control. Let's also say that rather than dividing your chakra evenly among the copies, or giving each copy its own limited supply, all of the copies remain connected to - and can draw on - the original's chakra pool, using it both to sustain their own existence and power any jutsu they may perform. (Which latter could be used to explain why it's a kinjutsu; without proper coordination between the copies, it would be all too easy to overdraw the chakra pool in a fairly major way. That's fairly weak, but no more so than some of the elements of the more common models.)
Now, with that model in mind, let's imagine that Naruto is out somewhere in a fight, using dozens of kagebunshin as usual. Let's say that something goes wrong, and the original Naruto gets fairly definitively killed - head pulped by a boulder, or the like; he certainly doesn't get up again. (Or alternately, he's out on his own, and manages to get killed in a landslide or the like with no witnesses.)
But his clones don't disappear; they remain as viable as ever, and manage to win the fight.
It develops afterward that they are all still connected to Naruto's chakra pool; they're all Naruto, after all, and it's theirs as much as it is the original's. They can perform any jutsu he could, including kagebunshin to create more copies.
And they can all draw on the Kyuubi, which is still imprisoned within the seal - the seal which is inscribed on all of them.
This means that except for aging (if they even do still age, being made of chakra), what they have here is effectively an immortality technique unlike any other, workable only for someone with an essentially endless pool of chakra. It's easy enough to take out one copy, but as long as there's still at least one more Naruto somewhere in the world and he has enough chakra, he can create more - and with the Kyuubi to draw on, running dry is an unlikely scenario at best.
It also means that the Kyuubi is pretty much never getting out. Akatsuki's bijuu-extraction plan is very likely screwed; even if extracting the Kyuubi from a single clone would work, the process appears to be traumatic enough that the clone would pop as soon as the extraction got started, leaving nothing to extract from and aborting the process.
The possibilities are especially interesting if he manages to hide the fact that the original Naruto is dead; everyone's used to seeing his clones around anyway, some people may be more used to seeing the clones than the original, and it might be a good long while before anyone realizes that nobody has seen a Naruto they can be certain was the original in quite some time. (I have a partial scene in mind in which someone finally does notice this, years later.)
For an alternate opener to a fic based on the same concept, which might take it in a rather different drection at least at first, imagine that he's not alone when he dies; he's out with a team, and dies in combat, at a point where he happens to not have any other clones involved in the fight.
His team members win the fight, and take his body back to Konoha (possibly somewhat confused about the fact that the Kyuubi doesn't seem to be emerging, if they know about it) - only to discover that all the clones he left doing things in town are still there, and may not even have noticed that the original isn't a going concern anymore.
The most common explanation of how it works is that it evenly splits the user's chakra among all the copies. However, that doesn't seem to match very well with the way it's observed to be used, nor with Kakashi's ability (demonstrated during the Wave bridge fight) to create many more kagebunshin than Naruto with the same total amount of chakra, simply by being more efficient at applying it.
The most common explanations of why it's a kinjutsu are that it uses so much chakra (leading to chakra exhaustion or the like), and that the mental whiplash of regaining the memories of a popped or otherwise expired kagebunshin can be damaging, especially in extreme cases.
Let's consider a different model. Let's say that creating a kagebunshin does take a certain amount of chakra, and that you can waste more or less additional chakra in the process depending on your chakra control. Let's also say that rather than dividing your chakra evenly among the copies, or giving each copy its own limited supply, all of the copies remain connected to - and can draw on - the original's chakra pool, using it both to sustain their own existence and power any jutsu they may perform. (Which latter could be used to explain why it's a kinjutsu; without proper coordination between the copies, it would be all too easy to overdraw the chakra pool in a fairly major way. That's fairly weak, but no more so than some of the elements of the more common models.)
Now, with that model in mind, let's imagine that Naruto is out somewhere in a fight, using dozens of kagebunshin as usual. Let's say that something goes wrong, and the original Naruto gets fairly definitively killed - head pulped by a boulder, or the like; he certainly doesn't get up again. (Or alternately, he's out on his own, and manages to get killed in a landslide or the like with no witnesses.)
But his clones don't disappear; they remain as viable as ever, and manage to win the fight.
It develops afterward that they are all still connected to Naruto's chakra pool; they're all Naruto, after all, and it's theirs as much as it is the original's. They can perform any jutsu he could, including kagebunshin to create more copies.
And they can all draw on the Kyuubi, which is still imprisoned within the seal - the seal which is inscribed on all of them.
This means that except for aging (if they even do still age, being made of chakra), what they have here is effectively an immortality technique unlike any other, workable only for someone with an essentially endless pool of chakra. It's easy enough to take out one copy, but as long as there's still at least one more Naruto somewhere in the world and he has enough chakra, he can create more - and with the Kyuubi to draw on, running dry is an unlikely scenario at best.
It also means that the Kyuubi is pretty much never getting out. Akatsuki's bijuu-extraction plan is very likely screwed; even if extracting the Kyuubi from a single clone would work, the process appears to be traumatic enough that the clone would pop as soon as the extraction got started, leaving nothing to extract from and aborting the process.
The possibilities are especially interesting if he manages to hide the fact that the original Naruto is dead; everyone's used to seeing his clones around anyway, some people may be more used to seeing the clones than the original, and it might be a good long while before anyone realizes that nobody has seen a Naruto they can be certain was the original in quite some time. (I have a partial scene in mind in which someone finally does notice this, years later.)
For an alternate opener to a fic based on the same concept, which might take it in a rather different drection at least at first, imagine that he's not alone when he dies; he's out with a team, and dies in combat, at a point where he happens to not have any other clones involved in the fight.
His team members win the fight, and take his body back to Konoha (possibly somewhat confused about the fact that the Kyuubi doesn't seem to be emerging, if they know about it) - only to discover that all the clones he left doing things in town are still there, and may not even have noticed that the original isn't a going concern anymore.