If the Clans won at Tukayyid, I think that would be the start of the slow demise of the Inner Sphere.
The Clans would continue to push towards Terra until one clan conquered it and absorbed all other clans to form a Star League in it's image. The exact fate of the houses would depend on which Clan took Terra first (Warden or Crusader).
I don't think that the rest of the clans would have held back and watched the IS destroy whichever clan took Terra, that would go against their grand plan. Whichever Clan took Terra would instantly become one combined Star League force. The Inner Sphere forces that tried to trap the clan invader on Terra would be steam rolled from behind by the newly founded Star League.
I think a lot of the finger pointing, bickering, and inter-clan warfare (like the Refusal War) essentially came about because of the Clan loss at Tukayyid. It shook the Clans to their core and of course incompetence within the ranks had to be the cause. It caused the Clans to doubt their leadership and that caused the cracks to start and the fracturing to occur.
Granted, they never got a long to begin with, but mutual respect for Nicholas Kerensky's dream would have kept them at least willing to go through with the plan.
and without the pause in the invasion to give the IS time to try and upfit their units, plus the demoralizing loss to the clans, probably meant the IS forces would never fully recover. Afterall, in the eyes of the houses and IS forces, the Clans would still be an unstoppable force. The Clan loss at Tukayyid probably gave the IS a HUGE morale boost by showing the superior clans could be beaten.
I will say this though. The Clans were essentially bred and engineered for one sole purpose. To take back the Inner Sphere and be it's protector or supreme ruler (depending on which philosophy won). Either way, as time would go by, the newly established Clan Star League would probably go through a crisis of purpose at some point. I think it would be a matter of time before the new clan Star League would colapse into infighting (probably due to the opposite philosophy trying to usurp power).
It would be interesting to see an alternate timeline of novels dedicated to covering this scenario.
Edited by MeiSooHaityu, 29 December 2016 - 06:13 AM.