For Spanglish bein a major international language, that's doubtful outside the American continents; Australia in particular, and AFAIK Canada, have nothing like the US' huge Spanish-speaking
majority 
(if what I've heard is correct). Britain IRC is in about the same boat, and India having
the largest English-speaking community in the world would be heavily influential in the development of English.
Whoever suggested the dissolution of English as a cohesive whole is probably right, with a "High English" hanging around like Latin does today, an American "Spanglish", an Indian version (I don't know what it'd be like, I know few Indian peeps), and a roughly standard "Low English" spoken in England itself and the Oceanic colonies.
Mandarin is, as Leo pointed out, a bitch to learn. I had five-and-a-half years of it, and, while in the same amount of time I developed enough French to be able to go on exchange with little difficulty, could barely carry a conversation on a proscribed topic. Maybe if they adopted pinyin as the standard (as I understand it's currently taught alongside character), and became lighter on the tonal variations, it might gain more use as a world language.
-Though I always did like how they used literal translations of things.
I reckon Esperanto's a crock; from having learnt Latin and French and being a native English speaker, I can understand Spanish, yet Esperanto goes straight over my head. Whoever thought it up was on crack, IMHO. It's too forced and contrived, and attempts to combine too many disparate elements. If you want a bastardised European language, English is already there, so why make up another one?
AFAIK, Japanese and Korean don't match up. However I do see words from Japanese definitely leaking into English through the fanboy subculture, then trade links. The same would go for Chinese if it weren't so alien to European languages with its block-construction linguistic method.
Russian, a mate of mine who's Ukrainian can read Russian, so, maybe a pan-Slavic language might be appropriate, if, as Leo said, they can pull their demographics out of freefall. It'd be interesting what happened to all the other non-slavic European languages, like Greek, if they managed to survive.
Sum, a (further) bastardised English hanging around, with a simplified version of Mandarin gaining precedence as a trade language (depending on Chinese migration patterns; if they all stay home, it might just stay local), competing with the Spamericans' own bastardised English.
Africa & Middle-East, I got little clue, except that I know Arabic is kept relatively standardised by the Qur'an. Mebbe as Leo said, local variants taking precedence.
... And that's probably the worst-edited post I've made here so far...