Thassilon RISES! (some spoilers)

Ok, so has anyone contemplated while playing the AP the possibility of acutally letting Xin take the Sihedron, killing off all his enemies in his crystal palace, and as his city rises from the sea either escape or offer to aid him in some way?
At this point, he has no conception of time having passed and is somewhat nuts, but later on at the end of the AP it mentions that if Xin is victorious, and as he marches on Magnimar and prepares for a greater invasion of Varisia and other nations, he begins to realize what has happened etc, and while his mind might still be broken, he is fully capable of thought, etc, etc, and while not a monster like the Runelords, is suitably paranoid and rather pissed.

All this stuff is entirely up to the GM at this point, but damn, I'm thinking it could be a rather interesting adventure and possibly even a turning point for the PC's that they choose to work for Xin and rebuild ancient Thassilon and even hunt down the remaining Runelords. Could be an interesting campaign of aiding Xin as he begins to conquer not only Varisia but other realms as well. Who knows.

Anyone done something like this yet? Ive discussed the concept with some people, and it seems like a helluva lot of work for a GM to try and plan out, but it's doable.

You definitely could do that, and it would make a cool way to expand on the campaign. The problem is your PCs would already be nearly at 20th level. This, of course, would be a great opportunity to introduce mythic rules.

I will say though that, as written, my take on Neo-Xin is that he now despises fleshy life. The reason he has a clockwork army is because clockworks will never betray him, and thus are perfect. Living, breathing, thinking beings are flawed, and will all be eliminated in a perfect Xin-tastic world.

It's a shame, but the thing that I took from the AP the most was that Xin was really a truly tragic figure, becoming something he probably hated.
If you look at it in that vein, then he's probably better off dead.

He's most certainly a tragic figure, and the only non-evil BBEG to date. Also, now that he's Mecha-Xin, whatever was left of his humanity/sanity will probably vanish pretty quickly. In the same way that liches and vampires slowly but surely lose all traces of their mortal selves, I think Xin will embrace his clockworkiness and become a machine, mind body and soul.

I think you could definitely make a compelling post-campaign with him though, but as you said it would take a lot of work.

I love this campaign. So many different ways to resolve things, so many different places to take it. The ability to continue the campaign beyond the crystal palace is simply soo enticing.

This is honestly my favorite to date (Kingmaker is #2) though the reason may be more that I am a Thassilon junkie right now.