Because of Magyarization, Hungary had worse ethnic tensions before the war than Austria. I think with a late Central Powers victory, Austria would stand a good chance of holding together, but Hungary would have a good chance of collapsing. Towards the end of the war Austria-Hungary was militarily heavily dependent on Germany. Germany is going to want to focus its forces on France and Italy once Russia's wiped out. They're not going to want to police Austria-Hungary's internal affairs, and even if they did get drawn into that, I think it would be likely to increase pan-Germanistic sentiment.How so?
Hungary's ethnic minorities would probably be more comfortable with rule from Vienna compared to rule from Budapest, but the Hungarians wouldn't like that, and even if rule from Vienna was the lesser evil, I'm not sure ethnolinguistic nationalists would accept it with a late Central Powers victory.What does "collapse" mean? Is it brought back under direct rule from Vienna, reverting to pre-1867?
If France falls, maintaining the blockade of Germany would mean extending it to both France and Spain (or at least the northwest coast of Spain). Even if that doesn't lead to any other countries joining the Central Powers it would torpedo the British economy because the USA (and possibly countries in Europe) would retaliate with economic sanctions. America had a lot of trade with Britain, but Washington would not take kindly to being shut out of almost all trade with the mainland Europe.A victorious peace does.
There won't be any availability of the Entente to prevent the immediate resumption of trade. That's called being defeated.
South American countries will be straining at the leash to get exports to the Central Powers - they won, they have credit. In fact, Britain and France may face complete food disaster, their credit has crashed in defeat, their exchequers are in a disastrous position, and their trading partners are now looking to those whose credit is good.