The treaty offer is probably about what the pre-war expectation was: fight until the opposed state acknowledged your Lord as the First Star Lord. Then repeat until you have enough of a majority that the others have to accept you. Absent the Kentares Massacre, the political will to refuse might not exist in the battered Federated Suns of the late 2790s.
By around the mid-29th century I'm fairly sure that the FedSuns would be itching to rise again. It's not a stable situation. But their opportunity to do so would depend on what the rest of the Inner Sphere would do.
Annexing the Federated Suns would pretty definitely leave the DCMS critically over-extended so that's not going to happen. On the other hand, the Combine seems to be fairly efficient at assimilating/suppressing populations during their advance on Lyran worlds so they might be able to impose a fairly effective regieme on their new holdings.
So lets look at this in time slices. In the first decade of the 29th century the FS is probably focusing what remains of the AFFS on holding back the Capellans, with a side-order of piecing their economy back together with whatever surplus they can scrape together. The DCMS, bolstered by their new province's industry (against which is the need to garrison it), shifts focus to the Lyran Commonwealth. Given how well they did in canon where they were getting kicked hard by the AFFS and still managed sizeable advances, I think it's safe to say that considerable gains are made at Lyran expense, particularly since the Free Worlds League is also hitting the Lyrans hard.
By the second decade, I think it's likely that Ilsa Liao, being a pragmatist, would have made peace with the Federated Suns in order to concentrate her efforts against the Free Worlds League and Draconis Combine. Other than Chesterton, the Federated Suns doesn't have much that she wants, and she might well have that by this point. The question is, does she make Minoru Kurita an offer? She was willing to cede her claim to the Davions, her ancestral enemies, whereas there were no major hostilities to the Combine. Ultimately I think it would depend on how the 'Kurita Star League' had treated the Federated Suns: if they gave more than lip service to the notion of the Combine being first among equals as the Hegemony had been rather than treating it as a conquered province, I think Ilsa Liao would be willing to offer Minoru her vote in return for quite minor concessions.
Even the DCMS is probably exhausted by the mid 2810s, but the Combine is almost certainly the strongest state by a fair margin. The Lyrans might well accept a peace treaty and reform the Star League Council, accepting the Kurita-controlled majority electing the elderly Minoru Kurita as First Star Lord. Isolated, Thaddeus Marik would probably be faced with a choice between rejoining the Star League as arguably the second most powerful state... or being forced to rejoin after another deblitating war.
Jinjiro dying on a battlefield before this point would probably be good for the Combine. It's unlikely that Minoru would live far into the 2820s (his father and grandfather lived to be 120, his sons were 94 and 84 when they died, and probably would have lived longer were it not for insanity in one case and an assassin in the other). Jinjiro on the Star Lord's throne... is not good news. Zabu, on the other hand, would probably be quite capable.
Who have I missed? Well Jerome Blake might well still be alive - he only died in 2819 so there are reasonable odds of living long enough to see the Star League reborn, which would probably lead to Conrad Toyama taking a different route with control of ComStar. And more than a thousand light years distant, the nascent Clans are still fighting to take control of the Pentagon.
