IMHO the Hungarians will get out and make the best deal they can. They can let most of Croatia go, perhaps keeping an outlet to the sea but ensuring that the territory they keep is overwhelmingly Magyar in population. Likewise given that it was "A-H" that started the war with Romania, they can probably cut a deal with the Romanians that draws a border without leaving too many of the "wrong" ethnicity on either side of the line. A clear division is not possible due to the checkerboard pattern, there may be a population exchange. At this point the Hungarians are not going to want many non-Magyars (Croats, Serbs, Romanians) inside their borders. They really don't want them for cultural/racial reasons, and have seen what a mess trying to have a multi-ethnic empire is. Sure, they will want as much "historical" ground as they can get, but will have to settle for less.
The Germans are not going to feel the need to be harsh with Hungary, why not let them exit easily. Furthermore weakening Hungary could make them more attractive for a communist takeover, the Germans certainly don't want to see any more communist countries in Europe. Unlike OTL where the disruptions along land borders with Russia after WWI led to communist uprisings, not happening here to any extent - Hungary is solid, Romania is no worse off than it was before the war started, Germany is a winner. Austria may be "ripe" after this disaster, but Germany can simply step in and squash this - the Austrians may not love the Germans, but most would prefer Germany to a communist Austrian government.
The UK is screwed - the Med is closed to them, A-H is toast, the ANZACs have bailed. It will be clear very soon that the submarines in the Caribbean are British manned but Mexican flagged, and Mexico will be screwed - I expect they will bail from any alliance with the UK ASAP to avoid losing more territory to the USA. If Mexico disavows the subs the crews, in uniform or not, are now pirates which is not good for them as well as having no place to go when they run short on fuel or ammunition. Their only hope is to run back to the UK if they have the range.
Japan is now facing the USA, and the Pacific forces of France and Germany for starts. The ANZACs may join in against Japan at some point. The UK is going to have so much trouble close to home that any assistance it might give Japan in the Pacific is weak indeed. Things won't end quickly in the Pacific, or in Europe for that matter but the British, Mexicans, and Japanese drew to an inside straight and busted.