And then, depending on how the CNS is doing, he can deal with it in a range of ways, from internal subversion (so he controls all three sides of the war)
This strikes me as simultaneously the most likely option for Palpatine to try, and the least likely to succeed. We are pretty good at that whole 'Intrigue' thing, you know, and the CNS is our home turf. Especially if/when we bring Jango onboard as a Hero ally, I expect Palpatine & Dooku will have a much harder time manipulating him. Sure, they might try to stir up domestic trouble, but after we absolutely
eradicated both Death Watch and Black Sun, I'm not sure there will be too many folks in the underworld willing to risk it.
Not to mention, we kinda have a history of taking enemies and turning them into solid allies. Asajj and Jango are only the latest.
to letting either the CIS or Republic win and then the winner fights the CNS
This seems like Palpatine's most-likely fallback option, and perhaps the least likely to succeed. The longer the war rages, the better positioned we become, and the more likely we've undermined critical parts of his grand plan for the galaxy. Besides the prospect of Outbound Flight returning and throwing everything into chaos with news of extra-galactic invaders, we have
so many plates in the air to undercut his efforts. We got Seti Ashgad, we got the soon-to-be-decrypted Inhibitor Chips, we got Mother Talzin, we got Asajj, we should be able to save quite a few non-Jedi Force sects from his purges, and we're even on course to nab The Chosen One out from under his nose...
So yeah. By no means do we have everything sewn up, but the longer Palpatine takes, the better our position looks.
or having the CIS and Republic ally and fight the "common Mandalorian threat".
Depending on how the Jedi & Republic respond, this is probably my biggest worry. One possible solution: recruit more (non-Mandalorian) systems to the Neutral banner. Last turn we were worried about whether Corellia would imbalance the CNS by joining -- they're a 3-billion population behemoth, compared to Mandalore's 4-million pop total. This turn... that sort of imbalance might be just what the doctor ordered. Corellia is a Core planet with an
outstanding reputation -- even the Jedi were willing to let them maintain their own 'Jedi' Order, even turning a blind eye to the whole 'married Jedi' thing, without crying 'Sith!' and let slip the dogs of war. They're fairly stable, very wealthy, and decidedly inclined to be neutral. Sounds like our kind of planet.
That's not to mention Satine's own efforts. I expect that she'll become the face and voice of the anti-war faction in the galaxy, and her message will particularly appeal to the anti-war systems still in the Republic. If (when) those Senators and systems find themselves dissatisfied with Palpatine's overreach, Satine will be ready and waiting with a fresh invitation to join the CNS. We might peruse the 'Loyalist Committee' and 'Petition of 2000' pages on Wookiepedia for lists of potential allies.
The same is true for our efforts with the CIS. The Separatists started out with a pretty decent cause -- I mean, Episode I tells us as clearly as I can that the Republic's authority doesn't really cover much of the Outer Rim, and that the Galactic Senate is corrupt and incompetent. The original idea of the CIS was: if the Republic won't take care of us, let's form a government that will. The problem, of course, was that the Separatist idea was co-opted by 1) galactic mega-corporations who
liked the Senate's corruption and wanted to generate more of it, and 2) a Sith Lord who needed the Republic to militarize, and manipulated the CIS to wage bloody war.
That means there are
plenty of 'Separatists' who are dissatisfied with the current CIS, and would see the CNS as a more palatable/less militaristic option. Remember as well that
Ciaran was the one who funded the original 'Outer Rim Defense Coalition' that Dooku took over and turned into the CIS. That investment alone will have made us plenty of allies among the sectors of the Outer Rim.
Another possible way to quell fears of a resurgent Mandalorian Empire: move the CNS capital away from Mandalore. Sure, keep Satine as the secretary of state/chief ambassador, and keep Jango as 'Mandalore', but as more planets join up, move the center of power somewhere else.
@Whumbly's "Possible Future" omake mentioned Taris, and I gotta admit that I
love the idea. Taris is a nearby ecumenopolis that (four thousand years ago) boasted a population of 900 billion (yep, with a 'b'). It was destroyed by a Sith battle fleet trying to 'smoke out' Bastilia & Revan doing their 'Knights of the Old Republic thing. Despite resettlement efforts, Taris never really recovered, and is to this day considered a "faded" city-world.
I can't help but think it'd be so perfectly
Ciaran to decide that after four millennia of stagnation, now's the perfect time to fix it!
Better yet: she might actually be right. Sure, there's a war going on, but most of the galactic economy is 'business as usual', and everyone's getting a lot of practice at the whole 'repairing damage after a battle/orbital bombardment' thing. Plus, after four millennia, the Taris ecosystem will have long since recovered, including those legendary kelp farms that managed to feed 900 billion people back in the planet's heyday. It's in the middle of Neutral Space, and straddles the biggest super-hyperlane in the galaxy, the Hydian Way, so it's perfectly situated to become a major economic center and trading post.
Frankly, the biggest problem in Taris right now is underpopulation -- the lack of warm bodies to work on setting things right. Lucky for us, we happen to run the galaxy's biggest humanitarian organization, and have access to millions if not
billions of refugees. We play our cards right, we could probably jumpstart the planet's reconstruction with minimal effort. Divert some credits here, a few million refugees there... pretty soon: "you got yourself a stew going, baby!"