Your rhetoric is still ridiculous. Users upgrading to the next version of software from where they got it in the first place does not make them "rebels."
This is the part you don't seem to understand. "Bitcoin" is not a static protocol that Satoshi wrote down in a paper six years ago. "Bitcoin" is what the community decides it is. For example, Satoshi's paper does not include a 1 MB block limit, yet that is very much a part of "Bitcoin" today. There are countless other elements of the system that exist in the form they exist today because of specific software that its users choose. Bitcoin tomorrow will likewise in all probability be something different (if there is ever another hard fork; opinions differ but my guess is there will be).
As for the "minuscule CPU/GPU mining network," you are horribly confused about how mining works. A gazillion hashes/second doesn't make the network secure and in fact the number of hashes is completely irrelevant. What matters for the most part is the amount of electricity used and secondarily the cost of the mining equipment. For example 100 watts buys you something on the order of 200 GH/sec of SHA256D. The same 100 watts would buy you perhaps 300 hashes/sec of (to pick one with which I happen to be familiar) CryptoNight. These are approximately equal in value for mining; 200 GH/sec of one algorithm is not 2/3 of a billion times "more secure" than 300 H/s of another. These units are incomparable.
The current bitcoin network is about 150 megawatts. That's something on the order of a 1-2 million PCs using a CPU algorithm. At least until specialized hardware and mining farms developed, a bitcoin forked to a CPU/GPU algorithm would look a lot like a million bitcoin users all mining on their computers. Sounds pretty darn secure to me.
Again, the rhetoric is absurd. An upgraded version of bitcoin with a hard fork (it wouldn't be the first), used by the majority of bitcoin users, is not an altcoin, it is bitcoin. The users adopting it are not rebels, they are bitcoin users.
In your scenario, the cartel has announced its plan in advance and distributed its hard fork version to all the users. The rest of the community can do likewise. There need be no interruption.
Furthermore, under this wartime scenario transactions would likely voluntarily halt anyway, because no one could be sure that the original chain being jammed wouldn't turn out to be the surviving chain, so no one would accept payments that weren't mined on it. That would certainly be an inconvenience and damaging to bitcoin generally, but the cartel would have no advantage absent some ability to guarantee that their fork would succeed, which they can't do.